Intramolecular dynamics by photoelectron spectroscopy. I. Application to N2 +, HBr+, and HCN+

peer reviewedThe Fourier transform of an optical electronic spectrum leads to an autocorrelation function C(t) which describes the evolution in time of the wave packet created by the Franck-Condon transition, as it propagates on the potential energy surface of the electronic upper state. This correlation function is equal to the modulus of the overlap integral between the initial position of the wave packet and its instantaneous position at time. The original data resulting from an experimentally determined spectral profile must be corrected for finite energy resolution, rotational, and spin-orbit effects. The behavior of the system can then be followed up to a time of the order of 10 -l3 s, i.e., during the first few vibrations which follow immediately the electronic transition. The method is applied to photoelectron spectra and the results are compared to the available information on potential energy surfaces of ionized molecules, in order to study their unimolecular dissociation dynamics. In the case of the X 2Σg +, A 2Πu, and B 2Σu + states of N2 +, an oscillatory pattern is obtained for the correlation function. This indicates that the nuclear motion is taking place in a bound potential. Effects due to anharmonicity are visible in the case of the A 2Πu state. The study of the X 2Π state of HBr+ demonstrates the overwhelming importance of spin-orbit coupling when heavy atoms are present in the molecule. Finally, the method is applied to a polyatomic molecule. The potential energy surface of the B̃ 2Σ+ state of HCN+ is characterized by two energy minima separated by a saddle point. The corresponding band in the photoelectron spectrum is characterized by an irregular vibrational structure superimposed upon a broad continuum. A study of the correlation function shows that the wave packet undergoes a complicated, two-component motion: while oscillating across the saddle point, it spreads away at the same time along the dissociative degree of freedom. This gives information on the rate of energy redistribution within the molecule. © 1982 American Institute of Physics

Isobutyl acetate: electronic state spectroscopy by high-resolution vacuum ultraviolet photoabsorption, He(I) photoelectron spectroscopy and ab initio calculations

The high-resolution vacuum ultraviolet photoabsorption spectrum of isobutyl acetate, C6H12O2, is presented here and was measured over the energy range 4.3–10.8 eV (290–115 nm). Valence and Rydberg transitions with their associated vibronic series have been observed in the photoabsorption spectrum and are assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. The measured photoabsorption cross sections have been used to calculate the photolysis lifetime of this ester in the Earth’s upper atmosphere (20–50 km). Calculations have also been carried out to determine the ionization energies and fine structure of the lowest ionic state of isobutyl acetate and are compared with a photoelectron spectrum (from 9.5 to 16.7 eV), recorded for the first time. Vibrational structure is observed in the first photoelectron band of this molecule

Photoelectron spectroscopy of a series of acetate and propionate esters

The electronic state and photoionization spectroscopy of a series of acetate esters: methyl acetate, isopropyl acetate, butyl acetate and pentyl acetate as well as two propionates: methyl propionate and ethyl propionate, have been determined using vacuum-ultraviolet photoelectron spectroscopy. These experimental investigations are complemented by ab initio calculations. The measured first adiabatic and vertical ionization energies were determined as: 10.21 and 10.45 eV for methyl acetate, 9.99 and 10.22 eV for isopropyl acetate, 10.07 and 10.26 eV for butyl acetate, 10.01 and 10.22 eV for pentyl acetate, 10.16 and 10.36 eV for methyl propionate and 9.99 and 10.18 eV for ethyl propionate. For the four smaller esters vibrational transitions were calculated and compared with those identified in the photoelectron spectrum, revealing the most distinctive ones to be a C–O stretch combined with a C[dbnd]O stretch. The ionization energies of methyl and ethyl esters as well as for a series of formates and acetates were compared showing a clear dependence of the value of the ionization energy on the size of the molecule with very little influence of its conformation

Electronic state spectroscopy by high-resolution vacuum ultraviolet photoabsorption, He(I) photoelectron spectroscopy and ab initio calculations of ethyl acetate

Abstract: The high-resolution vacuum ultraviolet photoabsorption spectrum of ethyl acetate,C4H8O2, is presented over the energy range 4.5−10.7 eV (275.5−116.0 nm). Valence and Rydberg transitionsand their associated vibronic series observed in the photoabsorption spectrum, have beenassigned in accordance with new ab initio calculations of the vertical excitation energiesand oscillator strengths. Also, the photoabsorption cross sections have been used tocalculate the photolysis lifetime of this ester in the upper stratosphere(20−50 km). Calculationshave also been carried out to determine the ionisation energies and fine structure of thelowest ionic state of ethyl acetate and are compared with a newly recorded photoelectronspectrum (from 9.5 to 16.7 eV). Vibrational structure is observed in the firstphotoelectron band of this molecule for the first time

Photoionisation et impact électronique dans le disulfure de carbone

L’étude de l’ionisation de CS2 a été faite entre 10 et 14 eV par photoionisation (ionisation totale) et entre 10 et 20 eV par impact électronique avec analyse de masse (méthode RPD sur spectromètre de masse à temps de vol). Deux nouvelles séries de Rydberg de faible intensité convergeant à 12,92 eV ont été mises en évidence. Une comparaison entre l’intégrale des courbes d’impact photonique et les courbes d’impact électronique est donnée. L’attention est spécialement attirée sur les difficultés d’interprétation de ces dernières. Un essai d’interprétation des courbes d’impact électronique est donné pour les ions fragmentaires CS+ et S+

Photoelectron Spectroscopy: a new analysis technique.

Beside the IR-, Raman- and UV-spectroscopies the photoelectron spectroscopy becomes an important technique for the qualitative and quantitative analysis of unknown samples. Important informations related to the electronic and molecular structure can be obtained by this technique.Outre les spectroscopies IR-, Raman- et ultraviolette, ces dernières années s'est développé la spectroscopie photoélectronique, devenue une technique d'analyse indispensable. Des informations importantes liées à la structure électronique et moléculaire peuvent également être obtenues. Sous certaines conditions une analyse qualitative et quantitative sont possibles.Naast IR-, Raman- en UV spectroscopie is de laatste jaren de fotoelektronen spectroscopie een onmisbare onderzoekstechniek geworden voor de identificatie van onbekende stoffen. Onmisbare informaties in verband met de elektronische- en molekulaire struktuur kunnen door deze techniek worden verkregen. In bepaalde omstandigheden zijn ook kwalitatieve en kwantitatieve anlises mogelijk

Réactions ion-molécule étudiées par spectrométrie de masse entre 0 et 1 Torr. I. Disulfure de carbone

Ion-molecule reactions occurring, between 0 and 1 Torr, in the ionization chamber of a modified mass spectrometer are studied for CS2. It is shown that, contrarily to the literature available on the subject, secondary ions in CS2 are created from vibrationally excited CS2+ ions in their electronic state (FORMULE)These ions are formed through autoionization. C2S4 + ions have been observed. Rate constants for the primary ions have been calculated and reaction processes are established.Les réactions ion-molécule qui se produisent dans la chambre d'ionisation d'un spectromètre de masse spécialement modifié pour travailler entre 0 et 1 Torr, sont étudiées pour CS2. Contrairement aux données anciennes de la littérature, il est montré que certains ions secondaires sont créés à partir d'ions CS2+ dans leur niveau d'énergie électronique 2 nu et excités dans des niveaux d'énergie de vibration assez élevés. Ces ions sont formés par un processus d'autoionisation. Nous avons observé l'existence d'ions C2S4 + dimères de l'ion parent. Les constantes de vitesse de disparition des ions primaires ont été calculées et les modes de réaction de ces ions ont été établis.Praet M.Th., Delwiche J.P. Réactions ion-molécule étudiées par spectrométrie de masse entre 0 et 1 Torr. I. Disulfure de carbone. In: Bulletin de la Classe des sciences, tome 58, 1972. pp. 912-924

Photoelectron Spectroscopy: an analyzing technique for surface study.

The shift of electron binding energies can be measured by ESCA (Electron Spectroscopy for Chemical Analysis). This phenomenon is the basis of important data for structural analysis.Le déplacement des énergies de liaison des électrons est mesurée par ESCA (Electron Spectroscopy for Chemical Analysis). Ce phénomène donne lieu à des renseignements importants pour l'analyse structurale.Met behulp van ESCA (Electron Spectroscopy for Chemical Analysis) kan men de verschuivingen in de bindingsenergieën van elektronen meten. Dit levert belangrijke gegevens op voor de struktuurbepaling

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