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ABSTRACT: Photoacoustic Raman spectra of gaseous pyrrole in the 3504 - 3535 and 3068 - 3152 cm-1 energetic windows were measured, to obtain new information about the hot bands in the vicinity of the N-H(1) and C-H(2) stretch fundamentals, respectively. The observed vibrational patterns are characterized by sharp Q-branches, where the strong ones reflect the fundamentals and the weaker ones, as established from their temperature dependence, the hot bands. From the simulation of the observed spectra, the band origins and non-diagonal anharmonicities were determined. Comparison of the latter values to the anharmonicities, xij (i = 1, 2 and j = 16, 15, 14, 12, 11) obtained from anharmonic calculations at the B3LYP/6-311++G(d,p), B3LYP/cc-pVQZ and MP2/cc-pVTZ level, aided the tentative assignment of the hot bands. The retrieved parameters add new data to the extensive set of already known vibrational constants of pyrrole.
The Journal of Physical Chemistry A 11/2012; · 2.95 Impact Factor
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ABSTRACT: The N-H stretch overtones of pyrrole, a key constituent of biologic building blocks, were studied by room temperature photoacoustic and jet-cooled action spectroscopies to unravel their intramolecular dynamics. Contrary to "isolated" states excited with two and three N-H stretch quanta, the one with four quanta shows strong accidental resonances with two other states involving three quanta of N-H stretch and one quantum of C-H stretch. The inhomogeneously reduced features in the action spectra provide the means for getting insight into the intramolecular interactions and the factors controlling energy flow within pyrrole. The time dependence of the survival probability of the 4ν(1) N-H stretch, deduced from the vibrational Hamiltonian, shows an initial decay in ~0.3 ps with ensuing quantum beats from the N-H-C-H resonance and their decay with a time constant of about 5 ps as a result of weaker coupling to bath states.
The Journal of chemical physics 01/2012; 136(2):024313. · 3.09 Impact Factor
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ABSTRACT: Laser-based spectroscopies coupled with molecular beam techniques facilitated the monitoring of H fragments released in ultraviolet photodissociation of pre-excited isoenergetic vibrational levels of pyrrole. Most noticeably, there was an order of magnitude larger reactivity for an eigenstate primarily consisting of two quanta of ring deformation than for another with one quantum of symmetric C-H stretch. The dynamics, the intramolecular interactions controlling the energy flow, and the mode-selectivity within a medium-sized, ten atom molecule, is discussed.
The Journal of chemical physics 05/2011; 134(20):201104. · 3.09 Impact Factor
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ABSTRACT: The mechanism of H and D atom loss, following ultraviolet photolysis of methylamine-d(3), CD(3)NH(2), has been studied via electronic action and Doppler spectroscopies. The N-H bond is preferentially cleaved and the yield of both H and D photofragments increases gradually, but differently, as higher vibrational states on the first excited electronic state, A, are accessed, leading to some drop in H/D branching ratios. The average translational energies of the H photofragments are somewhat higher than those of D, implying lower energy content left in the internal degrees of freedom of the CD(3)NH than in the CD(2)NH(2) partner fragment. These results provide evidence for discrimination between the two channels and mechanistic insight into the N-H and C-D bond cleavage.
The Journal of chemical physics 06/2010; 132(24):244310. · 3.09 Impact Factor
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ABSTRACT: The molecular dynamics of methylamine, CH3NH2, was investigated via vibrationally mediated photodissociation. It was found that the ∼243.1 nm photolysis of initially excited N–H and C–H fundamental stretches and combinations and overtones of methyl deformation yields H photofragments. Surprisingly, the deformations promote the H atom release more effectively, implying mode-dependent enhancement of photodissociation in a relatively large molecule with a torsional degree of freedom. The H Doppler profiles correspond to low translational energies, supporting the dominant non-adiabatic N–H dissociation channel.
Israel Journal of Chemistry. 03/2010; 47(1):11 - 16.
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ABSTRACT: The probability of hydrogen atom release, following photoexcitation of methylamine, CH(3)NH(2), is found to increase extensively as higher vibrational states on the first excited electronic state are accessed. This behavior is consistent with theoretical calculations, based on the probability of H atom tunneling through an energy barrier on the excited potential energy surface, implying that N-H bond breaking is dominated by quantum tunneling.
The Journal of Physical Chemistry A 02/2010; 114(36):9623-7. · 2.95 Impact Factor
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ABSTRACT: A novel application of ionization-loss stimulated Raman spectroscopy (ILSRS) for monitoring the spectral features of four conformers of a gas phase flexible molecule is reported. The Raman spectral signatures of four conformers of 2-phenylethylamine are well matched by the results of density functional theory calculations, showing bands uniquely identifying the structures. The measurement of spectral signatures by ILSRS in an extended spectral range, with a conventional laser source, is instrumental in facilitating the unraveling of intra- and intermolecular interactions that are significant in biological structure and activity.
The Journal of chemical physics 08/2009; 131(2):024305. · 3.09 Impact Factor
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ABSTRACT: The N-H and C-D bond fission in partially deuterated methylamine, CD(3)NH(2), has been investigated using vibrationally mediated photodissociation. Jet-cooled action spectra and Doppler profiles of the H and D photofragments were monitored following approximately 243.1 nm photodissociation of the parent pre-excited to two, three or four N-H stretch quanta. The action spectra were analyzed in terms of simplified local mode/normal mode (LM/NM) and NM models, allowing band assignment and determination of the strong resonances involved in the coupling. The Doppler profiles show that the released H and D photofragments have low translational energy content and that the H is the dominant product, although its yield decreases as higher pre-excited N-H vibrational states are dissociated. The dynamics of the site-dependent bond fission in CD(3)NH(2) is discussed.
The Journal of chemical physics 05/2009; 130(16):164312. · 3.09 Impact Factor
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ABSTRACT: A first experimental demonstration, combining the methods of vibrationally mediated photodissociation (VMP) and ionization-loss stimulated Raman spectroscopy (ILSRS) for measuring cross sections for dissociation of vibrationally excited levels is reported. The action spectrum obtained in the VMP of methylamine exhibits enhancement of the H photofragment yield as a result of initial vibrational excitation and the ILSRS monitors the fraction of molecules being excited. The partial cross sections for H production out of the sampled vibrational states and the extent of mode selectivity were thus determined.
The Journal of chemical physics 03/2009; 130(5):054303. · 3.09 Impact Factor
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ABSTRACT: Coherent anti-Stokes Raman scattering spectroscopy (CARS) was used for detection of solid particles of explosives and related compounds. The CARS spectra were recorded in the fingerprint region and were shown to exhibit the strong characteristic features of spontaneous Raman spectra of the respective compounds. This study demonstrates the applicability of narrowband backward-CARS spectroscopy for detection of explosives and specifically of its preference over spontaneous Raman scattering. This method has the potential to be applied to remote sensing of hazardous materials.
Applied Physics Letters 07/2008; 93(4):041115-041115-3. · 3.84 Impact Factor
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ABSTRACT: The vibrational pattern and energy flow in the N-H stretch manifolds and the dissociation dynamics of methylamine (CH(3)NH(2)) were investigated via vibrationally mediated photodissociation. Action spectra and Doppler profiles, reflecting the yield of the ensuing H photofragments, versus near infrared/visible vibrational excitation and UV excitation, respectively, were measured. The jet-cooled action spectra and the simultaneously measured room temperature photoacoustic spectra of the first to third N-H stretching overtones exhibit broad features, somewhat narrower in the former, consisting of barely recognized multiple bands. Two phases of fitting of the spectroscopic data were performed. In the first phase, the raw data were analyzed to obtain band positions, types, intensities, and transition linewidths. In the second, the information derived from the first phase was then used as data in a fit to joint local mode/normal mode (LM/NM) and NM Hamiltonian parameters. The derived parameters predicted well band positions and allowed band assignment. The LM/NM Hamiltonian and the extracted Lorentzian linewidths enabled the determination of the initial pathways for energy redistribution and the overall temporal behavior of the N-H stretch and doorway states, as a result of Fermi couplings and interactions with bath states. The results indicate a nonstatistical energy flow in the V=2 manifold region, pointing to the dependence of the coupling on specific low order resonances rather than on the total density of bath states. The Doppler profiles suggest lower average translational energies for the released H photofragments, in particular, for V=3 and 4 as compared to V=1 and 2, implying a change in the mechanism for bond cleavage.
The Journal of Chemical Physics 05/2008; 128(15):154319. · 3.33 Impact Factor
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ABSTRACT: The first overtone region of the C-H stretching vibration of 1,2-trans-d(2)-ethene (HDC=CDH) was monitored via jet-cooled action spectroscopy and room temperature photoacoustic spectroscopy. The spectra include a strong band, which we assigned as the nu(1)+nu(9) C-H stretch vibration, and five additional bands related to transitions to coupled states. The spectral features were modeled in terms of a six-state deperturbation analysis, revealing the energies of the zero-order states and the relatively strong couplings between the initially excited nu(1)+nu(9) state and the doorway states. Considering these energies and the fundamental frequencies of 1,2-trans-d(2)-ethene and presuming that only low-order resonances are involved in the couplings enabled the assignment of the states. The analysis also allowed obtaining insight on energy flow and to find out that the energy oscillations between the C-H stretch state and the doorway states occur on a subpicosecond time scale.
The Journal of Chemical Physics 04/2008; 128(11):114305. · 3.33 Impact Factor
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ABSTRACT: Vibrationally mediated photodissociation has been shown to control bond cleavage in molecules and probe their dynamics on the ground and excited potential energy surfaces. The application of this method to two seven-atom molecules illustrates surprising vibrational energy localization in methylamine (CH 3 NH 2), a molecule with a torsional degree of freedom and unique information regarding intramolecular vibrational energy redistribution for the C–H methyl stretches of propyne (CH 3 C ≡ C–H).
Phys. Scr. 01/2007; 762020(33).
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ABSTRACT: We report the first experimental demonstration of vibrational mode-dependent enhancement in photodissociation and photoionization of a seven atom molecule, methylamine (CH(3)NH(2)). The fundamental C-H stretches and the overtones or combinations of CH(3) bends were prepared via stimulated Raman excitation (SRE) prior to their 243.135 nm one-photon dissociation or two-photon ionization. The photodissociation or photoionization of the vibrationally excited molecules was achieved via 10 ns delayed or temporally overlapping SRE and UV pulses, respectively. It is shown that bending modes are more effective than stretches in promoting photodissociation and photoionization, since their UV excitation is favored by larger Franck Condon factors. This behavior provides clear evidence for vibrational mode-dependence in a relatively large molecule with a torsional degree of freedom, indicating that these modes survive intramolecular vibrational redistribution on a time scale considerably longer than hitherto inferred from previous studies.
The Journal of Chemical Physics 11/2006; 125(15):151103. · 3.33 Impact Factor
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ABSTRACT: H and D photofragments produced via vibrationally mediated photodissociation of jet-cooled normal ethene (C2H4), 1,2-trans-d2-ethene (HDCCDH), and 1,1-d2-ethene (CH2CD2), initially excited to the fourth C-H stretch overtone region, were studied for the first time. H and D vibrational action spectra and Doppler profiles were measured. The action spectra include partially resolved features due to rotational cooling, while the monitored room temperature photoacoustic spectra exhibit only a very broad feature in each species. Simulation of the spectral contours allowed determination of the band types and origins, limited precision rotational constants, and linewidths, providing time scales for energy redistribution. The H and D Doppler profiles correspond to low average translational energies and show slight preferential C-H over C-D bond cleavage in the deuterated variants. The propensities toward H photofragments emerge even though the energy flow out of the initially prepared C-H stretch is on a picosecond time scale and the photodissociation occurs following internal conversion, indicating a more effective release of the light H atoms.
The Journal of Chemical Physics 11/2006; 125(13):133301. · 3.33 Impact Factor
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ABSTRACT: Mesenchymal stem cells (MSCs) seeded on three-dimensional (3D) coralline (Porites lutea) biomatrices were irradiated with low-level laser irradiation (LLLI). The consequent phenotype modulation and development of MSCs towards ossified tissue was studied in this combined 3D biomatrix/LLLI system and in a control group, which was similarly grown, but was not treated by LLLI. The irradiated and non irradiated MSC were tested at 1-7, 10, 14, 21, 28 days of culturing via analysis of cellular distribution on matrices (trypan blue), calcium incorporation to newly formed tissue (alizarin red), bone nodule formation (von Kossa), fat aggregates formation (oil red O), alkaline phosphatase (ALP) activity, scanning electron microscopy (SEM) and electron dispersive spectrometry (EDS). The results obtained from the irradiated samples showed enhanced tissue formation, appearance of phosphorous peaks and calcium and phosphate incorporation to newly formed tissue. Moreover, in irradiated samples ALP activity was significantly enhanced in early stages and notably reduced in late stages of culturing. These findings of cell and tissue parameters up to 28 days of culture revealed higher ossification levels in irradiated samples compared with the control group. We suggest that both the surface properties of the 3D crystalline biomatrices and the LLLI have biostimulatory effects on the conversion of MSCs into bone-forming cells and on the induction of ex-vivo ossification.
Lasers in Medical Science 01/2006; 20(3-4):138-46. · 2.00 Impact Factor
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ABSTRACT: The first in vitro study testing the effect of a natural mixture extract of quality elk velvet antler (QEVA) on the development of bone marrow-derived mesenchymal stem cells (MSCs) is reported. To examine cellular responses, MSCs were seeded on gold-coated glass surfaces and grown in a medium supplemented with QEVA extract or with the osteogenic agent dexamethasone (Dex), or in unsupplemented medium as control. The MSCs were analyzed by light microscopy and confocal Raman microspectroscopy at different time intervals in the culture. The microscopy revealed that the proliferation, up to day 4, of cells treated with QEVA is higher than that of cells treated with Dex or of the control group. Raman spectroscopy revealed deposition of hydroxyapatite (HA) mineral by cells exposed to QEVA and HA precursors in cells treated with Dex, but no mineralization in the control group. The extent of mineralization for MSCs treated with QEVA increased systematically with time, up to day 14. These results indicate that QEVA enhances proliferation and promotes differentiation toward osteogenic fate more effectively than Dex, suggesting that addition of QEVA to culture media might be advantageous to bone-tissue-engineering implications. Copyright © 2005 John Wiley & Sons, Ltd.
Journal of Raman Spectroscopy 11/2005; 37(4):480 - 486. · 3.09 Impact Factor
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ABSTRACT: In this study, micro-Raman spectroscopy was used, for the first time, to detect spectral changes between healthy and diseased skin tissues with bullous pemphigoid (BP). The spectral changes provide information about the biochemical alterations between normal skin and blistered and nonblistered regions in samples diagnosed histopathologically as BP. Raman spectra, characterized by many peaks, revealed the molecular composition of the different skin layers, stratum corneum, epidermis and dermis of normal skin. Comparison of spectra monitored at the dermoepidermal junction (DEJ) of healthy skin with those of blisters caused by BP showed evidence for large variations in the amide I and III regions. The alterations of the protein content, amide I and III, are a result of the appearance of immunoglobulin G (IgG) and fibrin, characteristics of BP. Indication for the disease at early stages was obtained from changes in protein content, evidenced in the measured spectra assisted by cluster analysis. The method employed here can contribute to the nearly real-time diagnosis and to a better understanding of the physical and biomolecular processes effected by BP, and might have implications on other skin diseases. Copyright © 2005 John Wiley & Sons, Ltd.
Journal of Raman Spectroscopy 09/2005; 36(11):1034 - 1039. · 3.09 Impact Factor
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ABSTRACT: Room-temperature photoacoustic (PA) spectra and jet-cooled action spectra of the first to third overtone regions of the ethyl C-H stretches in vapor phase 1-butyne, CH3CH2C[Triple Bond]C-H, were measured. Both the PA and action spectra exhibit a complex multiple peak structure being better resolved and more pronounced in the latter, due to inhomogeneous structure reduction. The observed manifolds were analyzed in terms of a simplified joint local-/normal-mode (LM/NM) model accounting for two types of C-H stretches (methyl and methylene) and for Fermi resonances between stretches and deformations. The retrieved parameters, used for calculation of the eigenstates, come from the best-fit parameters based on the diagonalization of the vibrational Hamiltonian in the LM/NM basis. The parameters were obtained by comparing the eigenvalues and the sum of the squares of the expansion coefficients of the eigenvectors of the C-H stretches of methyl and methylene to the action spectra peak positions and intensities, respectively. This approximate model vibrational Hamiltonian is proposed to explain most observed spectral features, corresponding to C-H stretch bands and to combinations of C-H stretches and deformations, indicating the importance of the Fermi resonance. The model was also applied to calculate the dynamics of the C-H stretching modes resulting from coupling with the deformations, implying rapid initial state decay on subpicosecond time scale. Decays of several picoseconds were found for complete transfer of probability from the initially prepared state of methylene and methyl to the counterpart LM states.
The Journal of Chemical Physics 09/2005; 123(8):084316. · 3.33 Impact Factor
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ABSTRACT: Vibrationally mediated photodissociation and room-temperature photoacoustic (PA) spectroscopy have been used for obtaining action (monitoring the yield of H photofragments) and absorption spectra of the second (3nu(1)) and third (4nu(1)) C-H acetylenic stretches overtone regions in propyne. The band contours appearing in these regions seem mostly regular even though they are perturbed, as expressed by the origin shifts in different K components, splitting of the K structure, and splitting due to resonances between neighboring states. Symmetric rotor simulations of the band contours of the PA and action spectra allowed extraction of the molecular parameters and rough estimates for the homogeneous broadening arising from energy flow to the bath vibrational states. We particularly benefited from the reduced congestion in the jet-cooled action spectra and their simulations, which enabled observation of yet unknown features in the vicinity of the 3nu(1) and 4nu(1) states. Particularly, the emergence of the new state in the 3nu(1) region was confirmed by the action spectra monitored at several differing jet temperatures, suggesting that it is a dark state in IR vibrational excitation that becomes brighter in UV excitation to the upper electronic state. The monitored and Gaussian-fitted Doppler profiles point to the release of H photofragments with low average translational energies, attributed to an indirect dissociation process occurring after internal conversion to the ground electronic state and isomerization to allene.
The Journal of Chemical Physics 07/2005; 122(24):244318. · 3.33 Impact Factor
