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IR - Science topic

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I know that NIR can be direct and diffuse, but I would like to know if the same happens with the rest of IR.
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I'm not an expert, but diffuse radiation is the one affected by atmospheric dispersion mechanisms, like Rayleigh dispersion. This mechanism is effective on wavelengths that are similar to the size of the molecules causing it. I think from some graphs like the one attached that some NIR may be dispersed also, i don't know what'll be the case for longer wavelengths. Besides this, the leaf wil be emitting on other IR wavelengths energy quantities related to it's temperature and emissivity. Hope some of this helps. Regards
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I have a very thin sample of BNNT that is heated up and I need to measure it's temperature using a long wavelength IR camera. This BNNT is of unknown emissivity and I currently unable to measure it using a spectrometer. My thinking is that I can attach or apply a layer of a material of known optical properties to the bottom of the paper so I can measure it's temperature instead. Since I will be applying a think layer, I am assuming the temperature would be the same. I am expecting the temperature of the sample to be between 300 and 500 degrees Celsius.
Now my question is what can I use? I found one Thermographic paint that I can use but the distributor is in Europe and I am in Canada, so it would take some time to obtain the paint. I am looking for other alternatives before making a decision.
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Hello, the absolute temperature measurement of your material with a thermal camera will be quite tricky. It's designed for non transparent object with emissivity spectra similar to "perfect grey body". You can use a really thin paint layer of known emissivity just like you have mentioned. Just be carefull. This paint will change the mechanical properties of your material and can break when temperature changes. At 500degrees you can expected also some chemical reactions between paint and material.
You can also carry on with another aproach:
Heat your material to known temperature and measure it with IR camera as fast as you can. You can create a calibration table for different temperature and then it will be easy to calculate aprroximate temp. of your material.
You can also use really small SMD thermistor connected to your material with silverpaste and some glue and then use IR camera just for relative temperature measurement.
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If a thermal camera specifies minimum focusing distance as 20m/50m (based on the lens), it means that the bare minimum distance required to provide parallel beam on to the lens is 20m/50m to form image on to FPA.
As collimators with off-axis parabolic mirror provides parallel beam of cavity sources, is it possible to use the IR collimators for calibrating thermal imagers?
Research paper/ technical note, if available in this regard is requested
Thanks
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Hi Nagarajan, Theoretically, you can move the target closer to the off-axis parabola to replicate a finite conjugate. However, the further the conjugate is away from infinity, the larger the aberrations become. The magnitude of the aberrations depend on the focal length of the collimator and the aperture of the camera lens you are using. You really need optical design software to quantify the aberrations. A simpler option is to not use the collimator but to set the target 20m from your camera. If you do not have access to a controlled area this long, it is generally easier anyway to set up a flat mirror approximately half the distance required and then the target can be placed close to the camera.
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I run the CD spectra of the modified and non-modified protein and the 2ndary are the same. However, there is a change in amide I in the FTIR results. Thus, the functionalization might be expected to change the secondary structure. Kindly any suggestions with references.
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I want to know the best technique that provides exact and reliable results on the chemical composition of a plastic product (geosynthetic product) with the concentration of each compound
what is the best technique among these techniques to detect the chemical composition of a plastic product based on PP: Chromatography, Thermogravimetry analysis (ATG) or Fourier transform IR spectroscopy (FTIR).
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In IR spectrum, each polymer have number of absorption bands. From those bands, how can I find the Characteristic band or a band that can be used to find out the presence of a particular polymer? Or Is there any important absorption bands or a band that best describes a polymer?
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The infrared spectrum of a polymer or rubber is a profile of its absorption characteristics plotted against infrared wavenumber (or frequency). It is generated when infrared radiation interacts with the molecular moieties that constitute the polymer or rubber material. It is a distinctive property (a “fingerprint”) of the polymer or rubber sample in the form, manner and environment in which it is being examined. It is based on the absorption of infrared radiation at frequencies that match those of the normal modes of vibration within the macromolecule. These absorption features are characteristic of the molecular configuration, sequencing and conformation, and state of order. Absorptions by internal vibrations predominate in the mid-infrared region (ca. 4000–400 cm−1); they involve a few selected atoms in a molecular (functional) grouping, which is a sub-set of those constituting the macromolecule. External vibrations, such as lattice vibrations, which involve segments of macromolecules in crystalline regions, tend to occur at low wavenumbers (<400 cm−1). The intensity of an absorption band is, to a first approximation, proportional to the number density of vibrating species giving rise to that band. The intensity of an absorption band is related to the dipole moment change associated with the molecular vibration; if it is large then the band intensity will be high. Infrared spectroscopy is highly specific.
From Ref. (Infrared Spectroscopy in Analysis of Polymers and Rubbers)
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I’ve been doing some DFT calculations for the glyphosate molecule gaussian 09 program, and I need to have a reference FT IR spectrum in gas phase, thank you all
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I think you may find the experimental data from literature . For reference ir spectrum you can draw it with the gabedit or gausssum program from your frequency output file.
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Dear community,
we are trying to "debug" a liquid cleaning product formulation (substances added are known, s. below), which has developed crystals over time. We isolated, washed these and got IR spectra of the crystals and all ingredients that we use (see attachments). We are however still struggling to identify what our crystals could be and what could be reacting.
We know IR is limited in identifying a complete structure. But any further help in the interpretation is appreciated. In particular with regard to the strong, semi-sharp peak at 3281 cm-1. We interpret the main peaks with the bonding types O-H, C-H, C=O and C-O. The structure is similar to triethanolamine, except for the sharp O-H peak and the peak at 1738 cm-1. However, if the triethanolamine reacted with the esters or lactone we would expect a more intense peak.
Ingredients (in order of concentration):
  • Dimethyl glutarate (1,5-dimethyl pentanedioate)
  • Fatty acid esters
  • γ-Butyrolactone (Oxolan-2-on)
  • Ethers (3-butoxypropan-2-ol, [2-(2-methoxymethylethoxy)methylethoxy]propanol) and 2-methoxy-1-(2-methoxypropoxy)propane; 2-methoxy-1-[(1-methoxypropan-2-yl)oxy]propane)
  • Triethanolamine
Thanks for the support,
Nikolai
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That is the range for water molecules.
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Dears,
I face a technical issue of how to measure uniformity of infrared radiation on the target surface.
Namely, the setup is as follows. A halogen lamp is mounted at the end of the pipe-lightguide (see Fig. 1). When halogen is on radiation (visible light and infrared) is delivered to the target surface (c.a. 4x4cm). Total power of the radiation delivered to the surface is high (c.a. 200W which gives 13W per cm2). What I need to know is spatial distribution of the radiation on the target surface (to be able to find out how uniform it is). The measuring unit must withstand several seconds of measuring.
Several ideas and related issues:
1. IR camera could be placed at the end of the pipe. However, any reasonable camera will be burnt at once, at least oversaturated, as the power delivered is extreme.
2. Cover IR camera with a filter. This solution does not really work as the filter heats up and further emits radiation, i.e., I do not observe real distribution which would take place with no filter applied.
3. IR photodiodes. I imagine I could place several IR photodiodes at the end of the pipe but, again, they are highly oversaturated at once and filtering, again, does not really work.
4. Thermal-reactive paper/material(?). I am in trouble to find such a material which could withstand the power needed and provide any reasonable resolution.
5. ...?
Do you have any ideas on that?
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Gerhard, Aparna, thank you for the suggestions!
First, bolometers. As far as I have gone through the topic, it looks like a bolometer can measure the power of incident radiation, but not really its distribution. For the power mesurement we successfully use much cheaper equipment (water cooled sensors are enough).
The chopper wheel - it makes sense of course. However, to use such a wheel I need some space around the output of the pipe, so the wheel shall be mounted not under the pipe but at its side. This is very problematic as the system presented in Fig 1 is an internal part of the greater machine and access to the output of the pipe is very limited in terms of space.
A pinhole diaphragm - this idea we have tested in real. However, here, we faced several issues (e.g., mirrored surface of the diaphragm may change the distribution of radiation as it changes the lightpaths inside the pipe, so the real target may "see" other light distribution than the detector beside the pinholed diaphragm). But we will test that further.
Thank you!
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I have just started using ORCA and was following a YouTube tutorial series by Dr. S. Kishor => https://www.youtube.com/playlist?list=PLJIwRG-f5Gjd95jUG4cGjfSxs2gQfQAza
I'm using ORCA 5.0.3 on windows 10 with an i5 9400 processor and 500 GB A2000 Kingston RAM. In the 16th video of the series, I was introduced to IR frequencies calculation with geometry optimization with the following input -
# avogadro generated ORCA input file
# Basic Mode
# GeomOpt + Freq for Acetone
! RHF OPT FREQ 6-311++G**
* xyz 0 1
C -3.50986 2.85550 -0.14979
C -2.02053 3.03306 -0.02862
H -3.77767 1.82632 0.10157
H -3.82355 3.06176 -1.17685
H -4.01762 3.55239 0.52151
C -1.41776 2.78670 1.32795
H -1.61034 1.75505 1.63245
H -1.85017 3.48112 2.05247
H -0.33688 2.94710 1.28593
O -1.32971 3.36340 -0.99127
*
Now, when I'm opening the output file (.out) using Avogadro 1.2.0, the molecule was loading, but the frequencies were not loading. I checked the output file, and they were there but were not coming in Avogadro (should render automatically while opening the output file). I opened the Vibration toolbar from the settings of Avogadro to find they were not loaded. Can anyone help me how to view the IR frequencies generated from ORCA in Avogadro or other software?
N.B. - I found a discussion in the ORCA forum about OfakeG which can convert the ORCA output file into a Gaussian output file and I used that to covert as I have institutional access to Gaussian and GaussView (https://orcaforum.kofo.mpg.de/viewtopic.php?f=8&t=5018&p=21189&hilit=OfakeG#p21189). I followed the documentation but I was unable to convert the file type. I got an error saying the application couldn't find the file.
Enclosed:
1) Output File
2) Screenshot of Avogadro window
3) Screenshot of OfakeG application window
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As can be seen from the OfakeG screenshot, you didn't successfully convert the ORCA output file. You need to manually remove the double quotation marks from the automatically generated path, otherwise OfakeG cannot find it.
In addition, you can directly use Multiwfn (http://sobereva.com/multiwfn) to plot IR spectrum. See example in Section 4.11.1 of Multiwfn manual, you simply need to replace the Gaussian output file in this example with ORCA output file.
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My Hg/HgO standard electrode working properly . But It showing resultant current lesser than the Standard Calomel Electrode . Why ? drop your ideas ....TIA
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Arunkumar Gunasekaran you have not given much details of your experiment, electrode arrangement and electrochemical technique, but you should check the distance of your reference electrode, as well as the conductivity of the solution, also the sweep speed in case of CV. Because these are factors that can lead to a high iR drop. If you have the working and reference electrodes at a large distance, then the iR drop can be significant, same as at low conductivity and and very high sweep speed.
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As per literature,
"The net peak heights were determined by subtracting the height of the baseline directly from the total peak height. The same baseline was taken for each peak before and after exposure to UV.
The carbonyl index was calculated as: carbonyl index = IC/IR(100),
where IC represents the intensity of the carbonyl peak and IR is the intensity of the reference band."
Now, how do I substract the baseline height from the peak height???
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Dear Gitashree Gogoi,
I suggest you to calculate carbonyl index according to the method explained in the attached article. I hope it would be useful.
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Hello all,
I want some recommendations for spectrometers of UV to near IR (230 nm to 900 nm), with High resolution, have a good price, can distinguish between second and third harmonic, and are easy to use.
Thank you.
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Avantes spectrometer is highly recomnded in terms of product price and benfits
you can perform easily spectral scanning.
If you are interested in photon counting and high resolution Andor is one posibility, but you should know your need for that.
Good luck,
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I am preparing polymeric blends from recyclable materials. What are the characterization techniques that should be used and how to prepare the samples (IR, DRX, SEM, TEM, etc)? Could you suggest technical sources and papers/books?
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Thank your for your answer! I'm going to read te papers.
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Hello, I am a student researcher trying to export multiple spectra as .csv files (for graphing in Excel) in the Perkin-Elmer IR software. When I open an exported .csv file in Excel, it displays the y-values (%T) with only digits before the decimal point. I would prefer to have digits after the decimal point as well, as the graph is not very fine, and jagged. I have tried configuring the settings within the software, specifically changing "Decimal Places Y" in the Data options of the Export Setup. However this seems to have no effect on the exported data. How can I fix this? Thank you for your help.
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Very sorry for you having to use Excel for spectra processing. What about using the free optical spectroscopy software http://Spectragryph.com ? It will directly load the Original *.sp files from Perkin Elmer, and has plenty of functions for spectra visualization, processing and conversion. Just saying...
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Is OH bending IR band in PVA is related to inter/intermolecular hydrogen bond? why does it disappear on blending with another polymer?
Can anyone suggest a suitable reference?
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Sea surface temperature, chlorophyll, winds, altimetry observations are done by NASA, ESA, JAXA, ISRO and a few other government institutes. Commercial satellite data providers provide very high-resolution earth observation imageries in optical, IR or UV spectrum. Are there any commercial satellites that provide SST or Chlorophyll data?
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Hallo,
I've a HHG setup, but the IR filter is broken. This means that the entire IR intensity hits the CCD camera and would destroy it. Because a replacement filter needs a few weeks to arrive, I'm wondering if anyone has an idea how to cheaply/DIY block the IR in the vacuum before the CCD.
Many thanks in advance
Greetings
Konstantin
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I'm not too familiar with your setup, but would a sheet of aluminum foil do the trick?
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How can I observe moving cells without visible light? I tried with IR LED and an IR sensitive Bresser ocular camera, but the iR light was too weak.
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Primary answer :
The digital camera has Infrared blocking filters.
First, remove the filter which is on the digital camera close to the sensor.
The microscope must own hight quality optical elements.
Hope it solves the problem,
ALbert
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Pulse oximetry works by sending red and infrared light through blood vessels and measuring the absorption of the two wavelengths of light by hemoglobin. Blood also contains other proteins such as heme peroxidases which also absorb light at slightly different wavelengths. However, given that Hemoglobin is present in a much larger concentration, would it even be possible to detect other heme peroxidases through the method used in pulse oximetry even if they had different peaks?
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It is a novel question no doubt . Please go through -https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwi65a_Jsv_1AhUfzzgGHQ-YCZkQFnoECAYQAQ&url=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fbooks%2FNBK470348%2F&usg=AOvVaw2_r6r3aQVdi6yRm0mrBW_s in detail . If the condition of pulse oximetry satisfies for the detection of other heme - peroxidases .
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I want to briefly know, how theoretically IR and Raman spectrum of a particular optimised structure is estimated using DFT. Actually I want to know what is the basic theory behind this in a brief way.
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It is indeed hard it is to explain it briefly. Basically, you have to change the displacement of a given atom, this changes the electric field and generates a force (k), which is related to the frequency in the FTIR. I may have oversimplified the process, and I am sure there are other ways to compute the frequency. You might be interested in this paper: https://hal.archives-ouvertes.fr/hal-00906659/document
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After doping a InN nanostructure energy gap reduces and also in Ir spectrum molar extinction coefficient value decrease. What are reasons behind this?
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@Chian Heng Lee ,I have calculated dipole moment it's value also changes after doping.
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This strange waveform appeared today while measuring the IR background. After changing many parameters and testing many times, I still only get this waveform.
Then, sample measurement did not yield the desired waveform, so what is the reason for this waveform? Is there something wrong with the machine?
Thank you very much
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In answer to your question, "Infra Red background of what?" The background, in the case of this instrument, is measured without anything in the optical path except air. In other words, the instrument is measuring the output of the Nernst glowbar (the ceramic light source). When one transforms the interferogram to its spectrum using the Fourier Transform, you get the gray body spectrum of the light source with two pronounced notches (dips) for the absorption of CO2 and H2O in the air. The background spectrum should produce a very large signal.
Regards,
Thomas Cuff
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the thin film shows negative absorption in the IR region while taking UV-Vis -Nir spectra.
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Kamal Bhujel As I said, it is not possible to measure absorbance - your instrument either measure transmittance or reflectance and converts it to absorbance.
Can you tell me what your sample is (what kind of substrate)? Is the light going through your sample? You also had to perform a reference measurement... is the instrument empty for this measurement, or do you insert the pure substrate? Or, by any chance, a mirror?
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I have the NMR and IR of an organic unknown. The percentage of C, H, and O, is 71.1, 5.22, and 23.68, separately. And what are its 2,4-Dinitrophenylhydrazone derivative and Semicarbazone derivatives?
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is that 4,4'-Dimethoxybenzil?
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Two different IR spectroscopy for the same molecule:
Note: The cyano stretching band should disappear upon cyclization of the molecule.
-The first IR spectroscopy (A) represents the cyano absorption observed in the 2190 cm-1 region.
-The second IR spectroscopy (B) represents two different stretching bands observed in the 2194 cm-1 and 2207 cm-1 regions.
Concerning the second spectroscopy (B), if the stretching band 2194 cm-1 represents the cyano group, then what functional group does the stretching band 2194 cm-1 present, or do these two stretching bands illustrate the same functional group.
Thank you for your help.
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The functional groups observed in IR spectroscopy around the region 2190 cm-1 and 2194 cm-1 is unsymetrical C≡C.
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Basically, I have this protein: and I wanted to run an optimization on it and get thermodynamics, IR, NMR in a solvent. I believe due to the protein size, Gaussian crashes. Is there another software I can use? Thank you.
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Gaussian
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Transmission-FTIR spectroscopy can be used to analyze analytes in aqueous solutions e.g. Proteins in a formulation. Critical step: In order to correctly analyze the structure of proteins, the buffer solution's spectrum needs to be subtracted from the spectrum of the sample containing proteins. However, due to differences in the amount of water that is present in each sample, the difference spectrum cannot be simply calculated by: Difference Spectrum=Protein Spectrum-Buffer Spectrum.
What is a correct method to calculate the difference spectrum for e.g. algorithm based on least squares? I have looked into many papers and the most frequent answer is that a factor is used in calculating the difference spectrum to ensure that the resulting spectrum has a 0 baseline between 1750-2000 cm-1. But using a factor results in negative peaks in the difference spectrum.
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Sven Delbeck If you used Beer's approximation for calibration (or chemometrics based on Beer's approximation), then I hope you used molar concentrations.
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infra red heating become more popular recently because of low cost energy and efficienty , Radiant IR-Heater Tube is the most useful technology to achieve this as i know, I'm interested to collect IR generated by this kind of IR-Heater Tube in a linear fresnel concentrator for Infra red Radiations to obtain a high temperature in a centrale cynlindrical surface. This kind of IR Concentrator Exists ? Some one can advice ?
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We have imidazole ring N and Imine N for coordinating to metal in 2:1 (L:M) ratio. Both are forming coordinate bind with metal. So two covalent bond is from 2 O atom of acetate group. And the complex found be 6 coordinated in this case? Is there any possibility for this. How can we confirm the structure from IR and TGA for this acetate groups?
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Dear Anjali,
As Florian mentioned, it is not easy to state an adequate answer based on limited data. Please can post a chemical structure?
I agree with Matheus, concerning specificity there are only 2 posisbilities: IR or NMR; XRD does not provide any molecular specificity at all. But you might get the periodicity, if (and only if) a somehow periodic structure will be formed.
(1) You might start with IR/NMR measurements using a series of different L:M ratios starting from 0. Then, you can assign which peak belongs to imidazole, which to imine, and which to the rest.
(2) If you increase the L:M ratio, new (IR) peaks will appear due to binding. Most like they will arise at a lower frequencies/wavenumbers than the corresponding peaks from the unbound moieties. However, there might be exceptions. In most cases stretching vibrations undergo a redshift due to binding, whereas deformation vibrations undergo a blue shift.
(3) After you have the peak assignment you can study the ratio of the peak areas in dependence of the L:M ratio. I expect that particular sturture of coordination strongly depends on the L:M ratio.
I compiled some examples of IR measurements focused binding.
It might be that not all publications are exactly dealing with imidazole or imine, but you will definitely find instructions and band assingments. Look also in the reference there. Remember temperature changes affect the binding equilibrium somewhat comparable than changing the L:M ratio.
Best regards
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I need a site where I can see 19F, 1H, 13C spectra of organic compounds.
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Shubham Gupta hi! Spectral Database for Organic Compounds (SDBS), Reaxys.
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I need to perform Thermogravimetric Analysis with Infrared Spectroscopy (TG-IR) for my samples I have checked analyticsir.in both CIMFR and NITT instutes TG-IR system not working. other than that I couldn't be able to find any other facility in India. Someone point me in the right direction. Thanks.
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Snehalatha V 5c/min upto 800c. N2 atm.
Thank you for the reply
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Can I get electroluminescence camera and IR camera , PV analyzer on rent for research work in India?
Can I get the access or work permission of solar simulator lab in India for research work in any institute?
and what can I used instead of EL camera?
please share the link.....
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may be
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Help me with the identification of an unknown compound, I have attached the IR spectrum.
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Yes. You are right, if your peaks around strong 1785 cm-1 stretching C=O is acid halide, and medium 2900 cm-1 stretching is alkane, medium 3100 cm-1 C-H stretching is alkene, strong range 1650 cm-1 C=O stretching is lambda - lactam, and gamma-1750-1700 & beta-1760-1730, and strong 1725-1706 C=O stretching is Aliphatic ketone or cyclohexanone or cyclopentenone.
On your spectrum graph you can show the specific wavelength no. of peaks with the help of instrument, then you get a better results in your research
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I have a sample with magnesium, potassium, phosphate and water. I have found a peak around 3750, is it possible to consider magnesium with OH bound in IR for this peak?
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Dear
3600–3750 cm-1 relate to the OH stretching vibration.
Reference: (The structural OH mainly appears as characteristic peaks in four regions, 500–720, 3600–3750, 4000–4600, and 7000–7600 cm−1 , corresponding to the OH bending vibration, the OH stretching vibration, the OH secondary combination vibration, and the OH overtone vibration, respectively, Development of FTIR spectroscopy Methodology for ... - MDPI https://www.mdpi.com › 11 ›)
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I have tried to prepare the Schiff base from tetraphenylcyclopentadienone and p-aminophenol using MeOH, AcOH, 2 drops of HCl, and short bursts of microwave radiation (800W, 3 secs for 1 min).
Although it was small scale, a product formed that was clearly a light violet color. Naturally, tetraphenylcyclopentadienone is black and p-aminophenol is actually a beige/light brown color (due to degradation from light).
The IR looks very messy and I cannot find a reference IR for this compound. Is there a chance that I have failed to actually produce the desired product due to the intense 800W Microwave radiation, or bad solvent system? Maybe the HCl was problematic? Maybe I should have used EtOH?
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Dear Aidan,
that's a very interesting technical question. I did a SciFinder search for the desired product (such compounds are also called tetracyclone anils) and found that it has not yet been reported in the literature. Do you have access to SciFinder? In that case you should run a search using the structural formula of your product and see what literature references could help you. I'm not sure if tetracyclone (= tetraphenylcyclopentadienone) undergoes normal Schiff base formation reactions. In most previous literature references the authors carried out reactions of tetraphenylcyclopentadiene with aromatic nitroso compounds.
Good luck with your work and best wishes, Frank Edelmann
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I am wondering if we make a quantitative measurement of metabolites with an IR spectroscopy such as FTIR?
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Take a look at these.
1. Baker, M.J., et al., Developing and understanding biofluid vibrational spectroscopy: a critical review.Chemical Society Reviews, 2016. 45(7): p. 1803-1818.
2. Durlik-Popińska, K., et al., Correlations between autoantibodies and the ATR-FTIR spectra of sera from rheumatoid arthritis patients. Scientific Reports, 2021. 11(1).
3. Fang, T., et al., Rapid Diagnosis of Type II Diabetes Using Fourier Transform Mid-Infrared Attenuated Total Reflection Spectroscopy Combined with Support Vector Machine. Analytical Letters, 2017: p. null-null.
4. Finlayson, D., C. Rinaldi, and M.J. Baker, Is Infrared Spectroscopy Ready for the Clinic? Analytical Chemistry, 2019. 91(19): p. 12117-12128.
5. Rüther, A., et al., Vibrational Spectroscopic Based Approach for Diagnosing Babesia bovis Infection. Analytical Chemistry, 2020.
6. Sharaha, U., et al., Using Infrared Spectroscopy and Multivariate Analysis to Detect Antibiotics’ Resistant Escherichia coli Bacteria. Analytical Chemistry, 2017.
7. Banerjee, A., et al., Rapid Classification of COVID-19 Severity by ATR-FTIR Spectroscopy of Plasma Samples. Analytical Chemistry, 2021.
8. Nogueira, M.S., et al., Rapid diagnosis of COVID-19 using FT-IR ATR spectroscopy and machine learning. Scientific Reports, 2021. 11(1): p. 15409.
9. Pokhrel, P., C. Hu, and H. Mao, Detecting the Coronavirus (COVID-19).ACS Sensors, 2020. 5(8): p. 2283-2296.
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So I was running an IR on a sample that I had thought (or rather hoped) was phenol (hydroxy benzene), but what came out was either trash and noise, or I simply did not have phenol. My professor and I were quite stunned as it showed no signs of organic peaks at all, especially no -OH peak near 3100. My professor suggested to run my reaction again, but sadly I do not have the reagents on hand at the moment and it will be some time before I get them.
The reaction I ran was one taken from an old book on recycling benzene waste. When I conducted it, I took a mixture of nitrobenzene and benzene waste and I added a random amount of relatively pure Fe2O3 and 13% Hydrogen Peroxide to try and oxidize anything in the waste to phenol or hydroxynitrobenzene. After I treated it with NaOH to make a phenoxide salt and then I did some work up to isolate. What I was left with was a nice white crystalline salt (or so I thought). But the IR says it contains zero organics as far as our IR machine can tell, and our machine is used daily if not hourly, and is kept in great condition.
If someone could help me understand what I have or teach/lead me how to identify inorganics, that would be very appreciated.
Because the attached picture is possibly hard to see small details, I have listed the peaks as well.
Peaks:
-610.07 cm^-1 transmittance: 60%
-635.08 cm^-1 transmittance: 79%
-1091.13 cm^-1 transmittance: 64/65%
Rizal Awaludin Malik After rereading my notes, I have come to realize that I distinctly changed my procedure because I was having trouble with the Iron Oxides previously mentioned. My pseudo-procedure looks more like this:
Fe + 2HCl -> FeCl2 + H2
2FeCl2 + Cl2 -> 2FeCl3
FeCl3 + H2O2 (13% aq) -> Fe(OH)3 + Reactive Species
And my idea was to combine the benzene/nitrobenzene wastes I had with the final reaction in the scheme (combining the reactive species) to try and produce hydroxylated benzene and nitrobenzene.
Some notes from my notebook leave me further puzzled:
"Smell of nitrobenzene and benzene has totally disappeared, and lots of gas evolution. A red precipitate (likely iron oxides) has formed at the bottom of the beaker. There is no longer 2 layers (2 phases) and the yellow color of the solution is very faint, where it was quite deeply colored beforehand."
I'm not sure what exactly happened but I have done a little bit of searching and came across Hexaaqua iron (III) chloride, which may be what I have crystallized out.
To explain further, after the whole reaction was completed, I filtered off the red precipitate and tried to crystallize out whatever product I had formed. When I did so, I was left with a pure white free-flowing powder. The powder seems hygroscopic in nature.
I will likely try this again, with pure benzene to see if the same result occurs.
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Aidan Bradley as we know the range 1085-1050cm-1 is for strong-
C-O stretching. This is a primary alcohol. You have a pick is the 1091.13 cm-1 so it is more likely that is indicating the presence of C-O stretching. The other two picks are 636.06cm-1 and 610.07 cm-1. We know 690-515 cm-1 range indicates the presence of strong C-Br stretching, which is a halo compound. So those two picks are indicating the presence of C-Br stretching.
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Hi All,
I want to use silicon wafers for my mid-IR imaging project. I have some specifications for them from my previous lab colleagues. In our previous lab we used to buy:
3” N TYPE <1-0-0> 1-50 OHM-CM 350±10µm SEMI-Std FLATS DOUBLE SIDE POLISHED.
However, getting exact specification is proving to be an hassle!
I am not sure about some parts of the specifications. Could you please help me with the following questions?
1) If imaging data is collected in transmission mode, does the thickness of the silicon wafer matter? What I mean is change in thickness from 300um to 500 um?
2) If the imaging data is collected in transmission, does it matter if the silicon wafers are single side polished or double side polished?
3) if the imaging data is collected in transflection mode single polished silicon wafer should be fine?
Thanks
Mugdha
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Dear Mugdha,
1) Ideally, silicon is not absorbing. However, yours is doped (“N type”) and has a comparably low resitivity (1-50 OHM-CM). This means that the free electrons will lead to absorption, and the thicker your wafer is the less light you get through. I would recommend > 10.000 Ohm cm.
2) Double side polished means that spectra of layers will show interference effects, but those can be treated properly (see e.g. https://www.researchgate.net/publication/340232874_Removing_interference-based_effects_from_infrared_spectra_-_interference_fringes_re-revisited). Single side polished substrates suppresses the interference effects, but causes scattering effects which lead to spectra that cannot be safely quantitatively evaluated,
3) Same problems like those under 2)
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Can we use I.R active modes ?
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There are two reasons why Raman might be preferred for a certain system over IR (or vice versa):
a) just convention. In this case, a standardbenchmark for the material quality has been defined based on the Raman (or IR) peaks, so in order to compare your material with others for a meaningful publication, you need to make this comparison.
b) One method is a lot easier to perform. While most materials have both Raman and IR active vibrations, one of them may provide an intrinsically higher signal/noise ratio and therefore be more suitable.
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Especially for Agriculture Field which one is better?
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Surely ultrasonic sensors have definitive edge over IR sensors..
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Can you calculate IR and IRR p-values and CI in SPSS without using a regression model such as Poisson? I have calculated the breast cancer incidence for various groups by hand using the breast cancer incidence rates of the entire population of a country as a reference. I have calculated the p-values and CI also by hand, but I would like to check this using an analysis in SPSS. Thank you in advance.
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Hello Rachel Dassen. Well, you could convert your hand calculations into SPSS syntax. But I'm not sure that's what you're asking.
Which method of adjustment are you using, direct or indirect? Can you share the data (including the standard population info) with us?
Why are you opposed to using a regression model if it gives the correct results? HTH.
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Hi,
I have recently completed my Ph.D. from the Department of Government and IR at the University of Sydney. I am currently looking for a Post-doc position in Europe. My proposed project examines religiosity and support for radicalism among the migrants in Europe.
To begin my journey as an academician/researcher, what scientific and transferable skill should I have? Knowledge or training on which quantitative or qualitative methods or data collection softwares will benefit me in future?
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Hi Saimum, congrats on getting your PhD done! It is a great achievement.
If you want to engage in a project on radicalism, religion, and migrants, I'd suggest looking at qualitative research methods a bit more, as you would most likely be interested in talking to people about their experiences. Some interview/focus groups training or experience could be beneficial. Sometimes you can find community-run projects to acquire those skills. Learning SPSS and Nvivo is always good.
In addition, there is a growing tendency in Political Science to be working on big data. I'd suggest you have a look at the existing projects in your area that you find fascinating and see what approaches and software they used and why, and decide for yourself if you want to study it in your own time.
I'd be happy to answer any questions, and good luck!
Best wishes,
Ana
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What are some of the advantages and disadvantages of studying political science/international relations rather than pure history? Which is more useful for contemporary policy makers?
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History is good as a basis for a professional follow up degree. Political science would appear to be more related to government work or possibly a law degree. Studying international relations is a great way to gain a deeper understanding of global issues. It's an intriguing and important subject which places great emphasis on economics, culture, education, and political science and examines the impact they have on society.
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IR 3 micron cut-on 4.2 micron cut-off
D*=10 ^12 is a reasonalby realstic value considering currently technology
if not MCT any other options
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The photoconductive detector with microwave bias gives a high performance front end for optical receivers. Its advantage over other detectors is a high S/N at low light levels for information bandwidths approaching a gigahertz. The full potential is reached when the volume of the phototransducer can be very small, which means with intrinsic photoconductors and a diffraction-limited optical system. By definition, photoconductivity is the increase of conductivity of a material because of the absorption of electromagnetic radiation. In an appropriate circuit, this change in conductivity controls the delivery of signal power to an output circuit. In contrast, capacitive contacts can be used with a high-frequency bias supply. In principle, it can also perform well with extrinsic photoconductors in spite of the increased size needed to give reasonable optical absorption
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hi!
I have the problem with infrared.
As I found the problem of Ir , I did monitoring energy and interferogram.
Surprisingly, energy value is zero and interferogram is like the picture I upload. I think this is the serious problem. Does anybody know why this is happened and what can I do for solving it?
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One reason might be the presence of impurity one suggestion I want to make you clean properly the sample cell and use fresh KBr and run the sample
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When I searched about IR drop in the 3 electrodes system, I found that there is IR drop from WE to RE like the image below.
But I can't understand. A lot of literature says current only flow between WE and CE. so, I think there is no current or flux between WE and RE.
Can IR drop (resistance) exist when there is no flux or Do I misunderstand ?
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In a modern potentiostat, there is indeed a negligible current (usually < 1 nA) between the WE and RE in the electric circuit outside the electrolyte. This ability of the modern potentiostat ensures the accurate potential measurement between the WE and RE when there is no current flowing in the WE or the electrolyte, i.e. the system is at the equilibrium or open circuit state. Under such conditions, the iR drop is zero because i is zero, disregarding the value of R.
However, under a dynamic condition, there is still a current flowing between the WE and the tip of the RE in the electrolyte, according to the distribution of the electric field (lines) between the WE and CE. Because the WE potential is measured against the RE, the electrolyte resistance, R, and the current, i, (driven by the CE) between the WE and RE produces the iR drop.
Therefore, my answer to your question is that there is no iR drop when there is no current flowing in the WE or the electrolyte. However, the iR drop is present when a current flows through the electrolyte and the WE.
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After the reconnection of software,
I found that the spectrum of ir is strange..
When I measured IR, It was found like the picture I upload!
Before this happening, this ir worked very well…
What do you think is the problem?
It’s emergency for me…
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Normalizing can solve the problem of the negative transmittance issue, but the original problem is not solved yet.
By the way, I found the problem by monitoring energy and interferogram yesterday. Energy value is zero, and interferogram spectrum is like the picture I upload. The normal case is that the energy value has the number and interferogram main peak has to be set to the middle. Does anybody have another idea about this problem?
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We have two samples. One in dry form and the second one is mixed in water. Which spectroscopy technique should be used to characterize these samples between Raman and IR?
Please provide the proper justification for the answer, if possible.
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As you put in your last comment, IR spectroscopy is not the best for samples in aqueous solutions. However, if your dry sample is somewhat of a coarse powder you might have problems to acquire good spectra (low signal-to-noise ratio).
You can circumvent this problem by using an ATR (attenuated total reflectance) accessory and drying your sample over the ATR crystal to create an uniform film. Since you can control the sample concentration in the solution and the volume of solution added onto the crystal, both quality, reproducibility, and comparison between samples is significantly improved.
We developed and applied this technique to analyse microorganisms (planktonic microalgae) in the paper linked below. There you can find a description of the method.
I hope it helps you!
Cheers!
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Which technique should be preferred between Raman and IR spectroscopy and why??
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Dear Arvind Kaushik , both FTIR and Raman are good characterization tools you can use to identify different molecules in a sample, but as stated by Pierre Caulet and Jürgen Weippert , the applicability of these techniques would depend on the kind of molecules you want to identify and the also the possible negative effects of the sample´s matrix, which could make difficult the identification process. This last issue would be more relevant in the case of Raman, since the laser source used to exciting the sample could also excite luminiscence effects from some sample´s components which could cause a strong background that would make identification more complex. These effects can affect more the Raman signal because it is usually orders of magnitude weaker than the FTIR signal.
Bear on mind, however, that new Raman instruments and appropriate set-up designs or the use of Surface Enhanced Raman Scattering (SERS) sensors can overcome most of these problems.
Hope this helps. Good luck with your experiments.
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why all spectra of metal complexes are shifted to a lower wavenumber and reduced in intensity?
By examining infrared (FT-IR) , does the opposite happen, that the shift is towards the highest frequencies?
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Dear Hussein, thank you for asking this interesting technical question. In the case of IR spectroscopy, it cannot be said in general that "all spectra of metal complexes are shifted to a lower wave number and reduced in intensity". This depends on various different factors such as the individual metal, the type of ligands, the oxidation state of the metal etc. As mentioned by Shafikul Islam the carbonyl ligand (CO) is a good example. Due to the possibility of pi-back-bonding the IR bands of CO ligands are normally shifted to lower wavenumbers as compared to free carbon monoxide (2143 cm-1). However, in the case of cationic metal carbonyl complexes, the carbonyl frequencies can be even higher than that of free CO. For a typical reference on this phenomenon please see this interesting research article (see attached pdf file):
Why Do Cationic Carbon Monoxide Complexes Have High C-O Stretching Force Constants and Short C-O Bonds? Electrostatic Effects, Not σ-Bonding
As mentioned by Corentin Lefebvre the IR spectroscopy of metal complexes cannot be fully outlined in a short answer. It would be helpful if someone offered a course on spectroscopic methods at your institution. For some very basic information please have a look at the following potentially useful link:
Fourier Transform Infrared Spectroscopy of Metal Ligand Complexes
Good luck with your work and best wishes, Frank Edelmann
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There is hydrogen bonding in the glycerol, If we have an IR spectrum of Glycerol then how we will interpret that hydrogen bonding is present there?
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Dear Iqra,
You may indeed be able to see H-bonding of glycerol molecules in condensed phases (solution or solid). They should show as shifts of the position of some IR bands (those implied in H-bonding) with respect to the position of these same IR bands in the spectrum of the isolated glycerol molecule, i.e. in the gas phase, or isolated in a rare gas matrix,... where there is no intermolecular H-bonds.
The attached file may be of help, showing the example of VOCs adsorption on ice, and the formation of surface H-bonds with surface FTIR spectroscopy.
Best wishes
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In calculated spectrum there should be one band at about 800-900cm^-1, but analyzing the experimental spectrum of gas CCl4 (link: https://webbook.nist.gov/cgi/cbook.cgi?Spec=C56235&Index=1&Type=IR&Large=on) there can be observed more peaks at higher wavenumbers. Could someone explain why there is such a phenomenon present?
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The double peak between 800 and 900 cm-1, which cannot be seen in the spectrum you referenced, is seen as a consequence of Fermi resonance between the F2-type C-Cl vibration and a combination band of the F2 deformation vibration and an A2-band; the presence of 35Cl and 37Cl, which leads to a number of isotopomers with reduced symmetry, does not manifest itself in the spectra. The rest are combination bands also with higher harmonics. Have a look at
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You will be familiar with spectroscopy in the visible and ultraviolet spectral range. In thisrange electronic transition are observed. The absorption of infrared radiation is the process that comes next at lower energies: theexcitation of vibrational and rotational transitions. The energy required for a transition is approximately a factor
of 10 smaller than for electronic transitions. The spectral region is adjacent to the visible spectral region and
extends from 0.7µm to 1000µm, which is the infrared spectral region. In most cases the region from 2.5 to
25µm is used.
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It is a type of radiant energy with longer wavelengths and this is what I can comment on your IR RADIATION question
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Hi researchers,
I'm building my setup for recording behavior and calcium imaging simultaneously of larval zebrafish. Thus, I need to use infrared LEDs to illuminate the fish for my high-speed camera to capture the image of behavior because visible wavelengths such as 450-500 nm would affect our fluorescence signal. Currently, I'm using a ring of infrared LEDs around my fish of 60W in total and a 60-degree lighting angle, as shown in the image. However, the powerful light source also illuminates the microscope objective above the fish, leaving a noisy background making our behavior tracking error-prone. However, I cannot move the relative position of fish, objective, and camera. Thus, I'm thinking about changing my IR illumination for better contrast. I would like to reduce the lighting angle to a smaller range so it does not illuminate the objective as much as the fish. But I do not know how to change the light path due to my lack of knowledge in optics.
I would really appreciate it if someone can help with this.
Bests,
Frederick Zhao
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if, per your diagram, the primary issue is speculated reflection from the conic portion of the objective down towards the camera, then you can eliminate that problem by putting a cylindrical sleeve around the objective that sticks down as far as the bottom of the objective. This will shadow the conic part and ensure no light is specularly reflected in the forward direction. For best results make the sleeve out of something black and not shiny.
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An information retrieval (IR) system is a set of algorithms that facilitate the relevance of displayed documents to searched queries. In simple words, it works to sort and rank documents based on the queries of a user.
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Do you know historical references about these preferences? IR and RAMAN are complementary vibrational methods. Also, I know the mechanisms and some data about the history and development in the last years. But...Is it about the accumulated information about IR?
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I use both techniques: the use of charts rather than detailed attributions mostly depends on the purposes of the research. In structural studies, I presented the detailed attributions of both Raman and IR spectra and compared them with computational spectra. In more analytical studies, where the spectroscopic investigation is a support for the application of a material (i.e. biomaterials, agricultural sciences, cultural heritage....), charts are to be preferred.
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Hi! I`ve got question about DESs. How can I proof the formation of DES? If speak about IR, which regions should I look at and which bands can indicate on the presence of hydrogen bonds? And one more question: the addition of water results full distruction of DES or water will only dilute DES? Is there any information about how much water I can add to the DES before it stop being DES and become "water and dissolved substances"?
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Dear Arina Levina thank you for your interesting technical question. The question would certainly get more qualified answers if you explained what you mean by DES. I had a hard time finding it out. When you check the Wikipedia entry on the abbreviation DES you find no less than 26 different meanings of DES on the English page, from "Data Encryption standard" to "Deep Eutectic Solvent" (https://en.wikipedia.org/wiki/DES).
Since you were talking about hydrogen bonds in your original question I assume that in your case DES stands for desloratadine, right?
In this context, please have a look e.g. at the following useful link which is freely available as public full text:
Improving mechanical properties of desloratadine via multicomponent crystal formation
For the stability of desloratadine in water, please also see the following relevant article:
Acid-base equilibria and solubility of loratadine and desloratadine in water and micellar media
It could also pay off to use the "Search" function of RG to find and access other useful references on this topic. Just search for "desloratadine" and then click on "Publications". This will result in a large number of interesting articles:
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Dear Researchers, I am asking for your recommendation about IR camera that can be used for measuring the temperature during the welding process.
Regards,
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Hi
Fluke camera is almost the best but it's a little costly however ensure that the camera measuring capacity could cover you welding temperature application
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  • I need suggestions.
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Clemens' answer is correct although it can be dangerous making assignments based on negative data. If the compound is as drawn then I would expect a good NOE between the methyl signals as Clemens suggests. In the other isomer, you would probably see an NOE to the olefinic proton from the acetyl methyl (although this will be weaker). I'm not sure which couplings Khushwant is saying is indicative (there is only one proton on the olefin). There might be a proton-13C coupling to the acetyl carbonyl which would be different in the two isomers but that is a hard experiment to perform and requires a good model.
NOE is the obvious solution to this problem.
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I am looking for a software (ideally free) which can simulate polarized ATR-FTIR spectra of a stretched macromolecule, that has a specific orientation with respect to the electric field vector of the incoming IR light.
So far I have only found softwares that can predict unpolarized FTIR spectra.
Thank you for your suggestions,
Edith Perret
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Yes, the program can simulate the reflectance for an arbitrary angle of incidence, arbitrary incidence medium and arbitrary orientation, provided you have either the oscillator parameters or the two principal components of the dielectric tensor function. Less information will not do the trick, since the spectra depend on both, the orientation of a transition moment with regard to the polarization direction and with regard to the interface between surface of the sample and the ATR crystal.
If an "unpolarized" spectrum is the same as a spectrum that does consists of more than one principal component, then in addition to peak values, bands can be shifted and shapes can be changed. These alterations are the stronger the stronger the underlying oscillators are. AFAIK Gaussian and Castep are not suitable for this job...
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how to characterized whether Fe3O4 or Fe2O3 is formed by reacting FeCl3.6H2O and FeCl2.4H2O(2:1) in the basic medium under a nitrogen atmosphere?
will it be characterized by using IR or UV spectroscopy?
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How about trying X-ray ( or electron) diffraction?
Best wishes,
Carlos
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Hi! I have an IR spectrum of product obtained from CO2 electroreduction in acetonitrile using sacrificial Zn anode. The product formed is normally zinc oxalate. However, at high current densities, glycolate or glyoxylate may be formed. Does the peaks at 1767 cm-1 and 1579cm-1 confirm the formation of any of these compounds? The spectra is attached here. Thanks a lot!
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I want to study this paper can you help with this?
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Hello,
in my experiments I use an IR camera with a fixed emissivity of 0.95 to monitor the surface temperature of an evaporating ethyl acetate droplet (1 ml). In order to obtain correct values, I wonder if anyone here might know or has a reference to the emissivity of ethyl acetate? Can it be somehow approximated ?
Kind regards
Philipp
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Measure the temperature with an RTD and match it to an IR image. Perform this at several temperatures and you have the emissivity. Post it on RG, as others may need it.
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I need to immunoprecipitate selectively the IGF1R and the insulin receptor from human source and thought of using antibodies aganist the anti-alpha subnits of each receptor. Any advice is important
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Looking for an antibody needs some input like what cells, host and the species reactivity etc.. Without which, any advice will be purely based on assumptions !!
In fact, there are several anti-IGF1Ra antibodies in market with product references, citations for the respective antibody and applications tested for, like in your case, immunoprecipitation !!
BW
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I am not familiar with solid state parameters especially in rectification ratio where my background was in biotechnology,.
Currently I want to calculate rectification ratio (RR) of my sample/device and plot some graph for my paper. However, I found it quite confusing with little to no basics. The formula for RR = IF / IR , where I can plot a graph RR versus V based on several papers that i refered. Unfortunately, I do not know how they got the value based on this table
My question is the graph that i plotted is very weird as i refered to other people's work as attached. And some paper mention use RR value above threshold voltage? I need guidance and help in calculation as well as plotting the graph RR versus voltage.
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Hello
You bring the forward and reverse biasing voltages to parallel column. Do the same for IF and Ir
Devide IF/IR call this REc.
plot Rec. versus V forward or reverse
good luck
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I need the "ACRYLITE IR acrylic 11460" for the light/dark preference test
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Hi Nancy,
You may make an inquiry at Alfa Chemistry, they offer kinds of materials.
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I have a ethanol-water 50% extract of mango peel. I purified mangiferin from the extract with filtration and precipitation. so i obtained a low concentrated extract which i want to se the IR spectrum and compare with the mangiferin IR spectrum. however, I would like to know what concentration should i achived to obtain a good IR spectrum from liquid samples (Standard and Extract), Also how many sample should I need in mL. Any advise would be really usefull. PD: I have not enough standard or extract to make a solid sample lecture with KBr.
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Mr. Maya,
First, there should be used CaF2 cuvettes transparent to IR irradiation within 4000-1200 cm-1. Therefore, the analyte should exhibit characteristic IR-bands within the latter region of the electromagnetic spectrum.
Second, there should be acumulated a large number of spectra (at about 250-300) in order to improve the S/N ratio, due to low concentration of the analyte.
Finally, there can be used KBr-cuvettes within the framework of a smaller number of scans (at about 100-150,) but operating with a higher concentration of the analyte.
An additional comment on: The concentration LODs, respectively, LOQs of the IR-spectroscopic quantitative analysis depends on the intensity of the characteristic IR-bands of the analyte. Therefore, there is needed an additional information about the molecular structure of the analyte, in order to, answer to your question of the amount of sample required for a reliable analysis by means of IR-spectroscopy.
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Dear all,
In vasp, we can use either finite displacement method (IBRION 5/6) or DFTP (IBRION7/8) to perform vibrational spectroscopy.
I am aware that currently vdw correction cannot be applied with IBRION 7/8, but other than that, could you please leave your comments on how to choose between these two approaches for my system? Will the results of the two be system-dependent?
Thanks,
Azade
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In general, both methods can give comparable accuracies but have their own advantages and disadvantages. In both methods, for calculating phonon modes, one needs to calculate the so-called Hessian of the potential energy or simply speaking the first-derivative of force on all atoms.
In finite-difference (FD) or frozen phonon method, this derivative is taken using the FD method. In other words, the program first calculates the force constants (F) for finite displacements of atoms (dx) and then approximates the dynamical matrix dF/dx as in any FD approach. This method's advantage is that one can implement it in any scheme, including DFT, GW, DMFT, hybrid-functionals, etc. The disadvantage is that it requires construction of multiple large supercells, and its accuracy is dependant on their sizes (the larger, the more accurate).
In DFPT, instead of directly calculating dF/dx, the program calculates the second derivative of energy with respect to such displacements. Within DFT, this can be treated using first-derivatives of charge density functionals and requires no supercell construction. Accordingly, the DFPT calculations are computationally much less demanding than the FD ones. As you may guess already, the disadvantage is it cannot work with any scheme other than DFT (as it is very difficult to treat any derivative of charge density non-locally).
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I'm stuck on how to and what constraint to be applied while using MCR for IR spectroscopy data. There are 3 types of constraint : Equality constraint, Unimodality constraint, Non-neagativity, and Closure constraint. Please help me proceed.
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Muhammad Ali Thankyou for the article recommendation.
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This is a compound mixture
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If you have only these three ingredients, you can measure HCO3- level via titration. Then it can calculate Na level accounts for NaHCO3. Na+ and K+ levels can measure using Flame Photometric method. You can deduct the Na level estimated for NaHCO3 from total Na level and calculate NaCl level. There are few other routes too.
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Setup
The refractive index of most optical materials is monotonically decreasing, sideways sigmoidal in shape, with its highest value (for the purposes of this discussion) at the short wavelength (UV/Vis) side and its lowest value at the long wavelength (IR) side. An example of Silica is shown in the attached figure as a reference.
We typically refer to the short wavelength cutoff as the electron-transition edge and the long wavelength as the multi-phonon edge. At each of these edges, the photon begins to interact with the lattice of the optical material: on the short (high energy) side, by exciting an electronic transition in one of the constituent atoms, and at the long (low energy) side by exciting a multi-atom vibration called a phonon. In each of these cases