A. F. Lago

Universidade Federal do ABC (UFABC) | UFABC · Center of Natural and Human Sciences (CCNH)

We propose a novel approach for an indirect probing of conjugation and hyperconjugation in core-excited molecules using resonant Auger spectroscopy. Our work demonstrates that the changes in the electronic structure of thiophene (C4H4S) and thiazole (C3H3NS), occurring in the process of resonant sulfur K-shell excitation and Auger decay, affect the...

The dissociative photoionization dynamics of the chloroacetone molecule (C3H5OCl) in the gas phase, induced by vacuum ultraviolet (VUV) synchrotron radiation in the range from 10.85 to 21.50 eV, has been investigated by using time-of-flight mass spectrometry in the photoelectron-photoion coincidence mode. The appearance energies for the most releva...

The gas phase acidities (GA) of 5,5-alkylbarbituric acids have been experimentally determined by electrospray ionization-triple quadrupole (ESI-TQ) mass spectrometry and by using the extended kinetic Cooks method (EKCM). The GAs of C-H (1330.9 ± 10.0 kJ mol-1) and N-H (1361.5 ± 10.5 kJ mol-1) deprotonated sites of bifunctional barbituric acid were...

State-of-the-art argon KLL Auger spectra measured using photon energies of hν = 3216 and 3400 eV are presented along with an Ar [1s] photoelectron spectrum (square brackets indicate holes in the respective orbital). The two different photon energies used for measuring the Auger spectra allow distinguishing between the shake transitions during the A...

Rationale: The class of active components of the group of β-lactam antibiotics is very important for several fields and applications, although their stability and radiation reactivity properties are not yet well understood. We have studied the interaction of an important building block species, the 2-azetidinone (C3 H5 NO) molecule, with monochrom...

The ratios of single, double, and triple ionizations to the total photoionization of the halothane (C2HBrClF3) molecule have been investigated by a single-photon ionization in the energy range from 21.21 eV to 320 eV. In the valence region, the multiple ionization results can be described by a sum of contributions generated from the shake-off and t...

A theoretical study on the structural, electronic and spectroscopic properties for the isolated chloroacetone (C3H5OCl) and its molecular cation was performed with ab initio and density functional theory methods. Two conformers were found stable for the neutral molecule, where the structure with the chlorine atom on the edge of a gauche/cis conform...

The infrared signatures of polycyclic aromatic hydrocarbons (PAHs) are observed in a variety of astrophysical objects, including the circumnuclear medium of active galactic nuclei (AGNs). These are sources of highly energetic photons (0.2–10 keV), exposing the PAHs to a harsh environment. In this work, we examined experimentally the photoionization...

The Si 1s⁻¹, Si 2s⁻¹, and Si 2p⁻¹ photoelectron spectra of the SiX4 molecules with X=F,Cl,Br,CH3 were measured. From these spectra the Si 1s⁻¹ and Si 2s⁻¹ lifetime broadenings were determined, revealing a significantly larger value for the Si 2s⁻¹ core hole of SiF4 than for the same core hole of the other molecules of the sequence. This finding is...

The gas-phase Proton Affinity (PA) and Basicity (GB) of 2-, 3- and 4-hydroxybenzophenone isomers have been experimentally determined by the Extended Kinetic Cooks Method (EKCM), using ESI-TQ Mass Spectrometry. Our results show that 4-hydroxybenzophenone isomer (PA = 912.6 ± 8.4 kJ·mol⁻¹) is in the order of 10 kJ·mol⁻¹ more basic than the 2- and 3-h...

The infrared signatures of polycyclic aromatic hydrocarbons (PAHs) are observed in a variety of astrophysical objects, including planetary nebulae, star-forming regions and circumnuclear of active galactic nuclei (AGN). These objects are also source of high energetic photons (0.2 to 10 keV), exposing the PAHs to a harsh environment. In this context...

Recent advances in X-ray instrumentation have made it possible to measure the spectra of an essentially unexplored class of electronic states associated with double inner-shell vacancies. Using the technique of single electron spectroscopy, spectra of states in CS2 and SF6 with a double hole in the K-shell and one electron exited to a normally unoc...

A combination of resonant inelastic x-ray scattering and resonant Auger spectroscopy provides complementary information on the dynamic response of resonantly excited molecules. This is exemplified for CH3I, for which we reconstruct the potential energy surface of the dissociative I 3d−2 double-core-hole state and determine its lifetime. The propose...

We present a comprehensive experimental and theoretical investigation on the LMM, LMN, and LNN normal Auger spectra of xenon, which reveal excellent agreement with theory when core-hole lifetimes of the two-hole final states are taken into account. Generally, the spectra turned out to be highly complex due to a strong overlap of the Auger transitio...

We present the hypersatellite Auger spectrum of neon which contains the decay transitions of the K−2, K−2V, K−2L−1, K−2L−1V, and K−1L−1V states. The Auger decays of these types of core-hole states show different line shapes and linewidths which can be distinguished due to the high experimental resolution available for the present experiments. The i...

Time of flight mass spectrometry, electron-ion coincidence and ion yield spectroscopy were employed to investigate for the first time the thiazole (C3 H3 NS) molecule in the gas phase excited by synchrotron radiation in the soft X-ray domain. Total Ion Yield and PEPICO spectra were recorded as a function of the photon energy in the vicinity of the...

Tuning hard x-ray excitation energy along Cl 1 s → σ ∗ resonance in gaseous HCl allows manipulating molecular fragmentation in the course of the induced multistep ultrafast dissociation. The observations are supported by theoretical modeling, which shows a strong interplay between the topology of the potential energy curves, involved in the Auger...

Using synchrotron radiation and high-resolution electron spectroscopy, we have directly observed and identified specific photoelectrons from K−2V states in neon corresponding to simultaneous 1s ionization and 1s → valence excitation. The natural lifetime broadening of the K−2V states and the relative intensities of different types of shakeup channe...

Theoretical and experimental studies on the energetics, structure and other physicochemical properties of neutral 1-phenylethanol (1OH), diphenylmethanol (2OH) and triphenylmethanol (3OH) and their corresponding deprotonated anions (oxyanions, formed by deprotonation of the OH group) are reported in this work. The standard enthalpies of formation i...

In recent years double core-hole states are intensively studied since their chemical shifts provide detailed information about initial-state and relaxation effects in a molecule. We derived the Si 1s−1, 2s−1, and 2p−1 binding energies as well as the Si 2s−2, 2s−1, 2p−1, and 2p−2 double-core hole binding energies of different SiX4 systems in order t...

We have investigated resonant Auger decay of xenon following photoexcitation of each of the three L edges under resonant-Raman conditions , which allowed us to characterize several higher Rydberg transitions. Relative intensities for spectator final states reached after L 1-, L 2-, and L 3-edge excitations are studied in detail. Thanks to state-of-...

Photoelectron photoion coincidence measurements have been performed for the thiazole (C3H3NS) molecule in gas phase, using time-of-flight mass spectrometry in the electron-ion coincidence mode and vacuum ultraviolet synchrotron radiation. photoelectron photoion coincidence spectra have been recorded as a function of the photon energy covering the v...

Aromatic Infrared Bands, the footprint of molecules like neutral and ionic Polycyclic Aromatic Hydrocarbons (PAHs), have been observed in several astrophysical environments. We present the experimental results of the photoionization and photodissociation of the methyl-benzene (or toluene) molecule, a basic unit for the methylated PAHs, using synchr...

Rationale: An interesting class of volatile compounds, the monoterpenes, is present in some plants although their functions are not yet fully understood. We have studied the interaction of the camphor molecule with monochromatic high-energy photons (synchrotron radiation) using time-of-flight mass spectrometry and coincidence techniques. Methods:...

Gas phase protonation enthalpy (proton affinity) and deprotonation enthalpy of paracetamol, PA = 909.4 ± 8.4 kJmol -1 and ∆acidH 0 = 1430.3 ± 8.8 kJmol -1 , have been experimentally determined by the extended kinetic method (EKM) using ESI-triple-quadrupole mass spectrometry. Gas phase basicity and acidity deduced from these experiments, GB = 869...

Dissociative photoionization of trifluoroethyl iodide (C2H2F3I) molecule has been investigated by electron-ion coincidence technique (PEPICO) and VUV synchrotron radiation. Mass spectra have been recorded for this molecule in the photon energy range of 10–22 eV. The molecular ion as well as cationic fragments have been detected and analyzed as a fu...

We present a series of photoabsorption and partial-ion-yield experiments on thionyl chloride, SOCl(2), at both the sulfur and chlorine K edges. The photoabsorption results exhibit better resolution than previously published data, leading to alternate spectral assignments for some of the features, particularly in the Rydberg-series region. Based on...

We report a study on the energetics and structural properties of naphthalene-based proton sponges and their corresponding protonated cations. In particular, we have determined the experimental standard enthalpies of formation in the gas phase at T = 298.15 K, ΔfHmo(g), for the neutral and protonated DMAN [1,8-bis (dimethylamino)-naphthalene], (221....

The anionic and cationic photodissociation from deep-core excited chloroform molecule has been investigated in the vicinity of the Cl 1s excitation edge. We used synchrotron radiation, time of flight mass spectrometry and ion yield spectroscopy. From our partial anion yield results we were able to observe for the first time the formation of the fol...

Photodissociation experiments have been performed for the parabanic acid (C3H2N2O3) molecule in vapor phase using time-of-flight mass spectrometry and synchrotron radiation in the VUV photon energy range. Electron ion coincidence (PEPICO) spectra and partial ion yields have been recorded as a function of the photon energy covering the 11–21 eV vale...

Two special dynamical transitions of universal character have been recently observed in macromolecules at $T_{D}\sim 180 - 220$ K and $T^{*}\sim 100$ K. Despite their relevance, a complete understanding of the nature of these transitions and their consequences for the bio-activity of the macromolecule is still lacking. Our results and analysis conc...

An experimental photochemistry study involving gas- and solid-phase amino acids (glycine, DL-valine, DL-proline) and nucleobases (adenine and uracil) under soft X-rays was performed. The aim was to test the molecular stabilities of essential biomolecules against ionizing photon fields inside dense molecular clouds and protostellar disks analogs. In...

We present experimental studies on the interaction of soft X-rays on gas- and solid-phase amino acids and nucleobases in an attempt to verify if these molecules can survive long enough to be observed or even to be found in meteorites.

We have carried out a study of the energetics, structural, and physical properties of o-, m-, and p-hydroxybenzophenone neutral molecules, C(13)H(10)O(2), and their corresponding anions. In particular, the standard enthalpies of formation in the gas phase at 298.15 K for all of these species were determined. A reliable experimental estimation of th...

Export Date: 10 November 2011, Source: Scopus

We present experimental studies on the interaction of soft X-rays on gas-phase and solid-phase amino acids and nucleobases in an attempt to verify if these molecules (supposed to be formed in molecular clouds/protostellar clouds) can survive long enough to be observed or even to be found in meteorites. Measurements have been undertaken employing 15...

Benzene molecules, present in the proto-planetary nebula CRL 618, are ionized and dissociated by ultraviolet (UV) and X-ray photons originated from the hot central star and by its fast wind. Ionic species and free radicals produced by these processes can lead to the formation of new organic molecules. The aim of this work is to study the photoioniz...

Full Title: Erratum: A photoelectron photoion coincidence study of the vinyl bromide and tribromethane ion dissociation dynamics: Heats of formation of C 2H3+, C2H3Br, C 2H3Br+, C2H3Br 2+, and C2H3Br3 (Journal of Physical Chemistry A (2006) 110A (3036)).

We have investigated the thermochemistry and ion energetics of the oxybenzone (2-hydroxy-4-methoxy-benzophenone, C14H12O3, 1H) molecule. The following parameters have been determined for this species: gas-phase enthalpy for the of neutral molecule at 298.15K, (Delta(f)H0(m)(g) = -303.5 +/- 5.1 kJ x mol-1), the intrinsic (gas-phase) acidity (GA(1H)...

We present experimental studies on the photoionization and photodissociation processes (photodestruction) of gaseous amino acids and nucleobases in interstellar and interplanetary radiation conditions analogs. The measurements have been undertaken at the Brazilian Synchrotron Light Laboratory (LNLS), employing vacuum ultraviolet (VUV) and soft X-ra...

An experimental study of the electronic excitation and ionic dissociation of two important classes of biomolecules–natural products (biogenic volatile organic compounds, VOCs, and volatile components of essential oils) and DNA and RNA constituents (aminoacids and bases) is here exemplified with recent results on the fragmentation of thymine and iso...

We present results on the valence level excitation, ionization and dissociation of adenine, using time-of-flight mass spectrometry and synchrotron radiation, in the vacuum ultraviolet (VUV) range of 12-21 eV. The measurements were performed using a gas-phase (Ne) harmonics filter in order to eliminate contributions from higher-order harmonics. Mass...

The p-aminobenzoic acid (C7H7NO2) molecule has been investigated at different levels of theory. DFT methods (B3LYP and PBE1PBE), second order Møller–Plesset perturbation theory (MP2) and composite ab initio methods (G3MP2 and CBS) have been employed, in conjunction with large basis sets. Important informations on the electronic structure and thermo...

Electron-ion coincidence technique (PEPICO) and synchrotron radiation have been employed in the study of the ionic fragmentation of epichlorohydrin (C3H5ClO) molecule. Total ion yield and mass spectra have been recorded for the first time for this molecule in the vicinity of the C Is, 0 Is and Cl 1s core excitation edges. We have found evidences of...

Chloroform (HCCl3) molecule has been studied using time-of-flight mass spectrometry in the multi-coincidence mode and synchrotron radiation as the source of photons in the range from 34 to 230 eV, which encompasses the valence level and the Cl 2p edge. Photoionization branching ratios have been measured under efficient ion extraction. Photoelectron...

Vacuum ultraviolet beamlines based on grating monochromators share the problem of high-order harmonics contamination. In the low-photon energy range up to 25eV, this problem may be overcome by letting the light beam pass through a high-pressure gas region. Here the photons with energies higher than the gas ionization threshold are absorbed and dump...

Photoionization of the limonene [C10H16] molecule was studied for the first time following C 1s ionization, using synchrotron radiation and time-of-fight mass spectrometry. As a reference for further analysis of the photon induced fragmentation of the limonene molecule, the He(I) mass spectrum was also obtained. Previously unreported singly charged...

The cationic and anionic fragmentation of dichloromethane (CH2Cl2) molecule have been investigated in the energy range of the Cl K shell by using synchrotron radiation, ion yield spectroscopy, and electron-ion coincidence spectroscopy. Total and partial ion-yield and mass spectra have been recorded as a function of the photon energy. We were able t...

We report on new soft X-ray photoionization studies of the amino acids l-alanine and l-proline. Total ion yield and mass spectra have been obtained in gas phase, around the N 1s and O 1s edges, using Time-of-Flight Mass Spectrometry and synchrotron radiation as excitation source. No site selectivity was observed in the ionic dissociation of the mol...

Threshold photoelectron photoion coincidence (TPEPICO) technique has been employed to determine accurate dissociative photoionization onsets for chloroform and 1,1,2,2-tetrachloroethane molecules. Our 0K onsets for these reactions are CHCl3+hv→CHCl2++Cl (11.500±0.007eV); C2H2Cl4+hv→C2H2Cl3++Cl (11.565±0.010eV) and C2H2Cl4+hv→CHCl2++CHCl2 (11.669±0....

The threshold photoelectron photoion coincidence (TPEPICO) technique has been used to measure accurate dissociative photoionization onsets of vinyl bromide and 1,1,2-tribromoethane. The reactions investigated and their 0 K onsets are C2H3Br + hnu --> C2H3+ + Br (11.902 +/- 0.008 eV); C2H3Br3 + hnu --> C2H3Br2+ + Br (10.608 +/- 0.008 eV); and (C2H3B...

Ionic fragmentation of the sublimated amino acid DL-proline has been studied using time-of-flight mass spectrometry and synchrotron radiation. Total ion yield and mass spectra were recorded in the 13 to 21.6 eV energy range. Partial ion yields have been calculated for the produced fragments and the results analyzed in a comparative way. Mass spectr...

The liquid phase equilibrium reaction of dihalomethanes (2CH2BrI ¢CH2Br2 + CH2I2) has been investigated by NMR spectroscopy, as a function of the temperature and initial concentration of the reactants. The equilibrium constants have been experimentally determined for this reaction from the profile of the NMR spectra. Heat capacity measurements were...

The ionic fragmentation of the chloroform (CHCl3) molecule has been studied along the Cl1s edge, using synchrotron radiation and a magnetic mass spectrometer. The following cations were observed: Cl+, Cl2+, CCl+, CCl2+, CHCl+, Cl3+, H+ and C+. While all ions are seen to be formed at the intense resonance which dominates the photoabsorption spectrum...

Recent advances in threshold photoelectron photoion coincidence (TPEPICO) make possible the analysis of several parallel and sequential dissociations of energy selected ions. The use of velocity focusing optics for the simultaneous collection of threshold and energetic electrons not only improves the resolution, but also permits subtraction of coin...

The dissociative photoionization studies have been performed for a set of dihalomethane CH(2)XY (X,Y = Cl, Br, and I) molecules employing the threshold photoelectron photoion coincidence (TPEPICO) technique. Accurate dissociation onsets for the first and second dissociation limits have been recorded in the 10-13 eV energy range, and ionization pote...

It is known that polycyclic aromatic hydrocarbons (PAHs) are mainly formed in the dust shells of late stages of AGB type carbon rich stars. After the ejection of H-rich envelope those stars become the proto-planetary nebulae (PPNs). The chemistry in PPNs has been strongly modified by the UV photons coming from the hot central star and by the X-rays...

Ionic fragmentation of the sublimated α-amino acids glycine, l-alanine, l-proline and l-valine has been studied using a time-of-flight mass spectrometer coupled to a He I lamp (hν = 21.21 eV). Partial ion yields (branching ratios) and kinetic energy releases for the fragments have been determined. The spectra basically resemble available mass spect...

The dissociative photoionization of the chloroform and chloroform-d molecules has been studied in the valence region and around the chlorine 2p edge. Time-of-flight mass spectrometry in the coincidence mode-namely, photoelectron-photoion coincidence (PEPICO)-was employed. He I lamp and tunable synchrotron radiation were used as light sources. Total...

A nebulosa CRL 618, uma proto-nebulosa planetária cuja nuvem molecular espessa envolve uma estrela B0, contém uma grande quantidade de C2H2 e CH4. Estas moléculas são consideradas os tijolos da criação de grandes moléculas carbonadas como os Hidrocarbonetos Policíclicos Aromáticos (PAHs). Esta nebulosa, por estar exposta a intensos campos de UV e R...