J. Heinesch

On the high-resolution HeI photoelectron spectrum of Cl2O

Abstract The high-resolution HeI (58.4 nm) photoelectron spectrum of dichlorine monoxide, Cl 2 O, has been recorded in the region of the four lowest-energy ionic electronic states. Formation of the ion in its ground and excited electronic states is accompanied in each case by vibrational excitation. In particular, the vibrational structure of the first and second excited states of Cl 2 O + is resolved. Analysis of the vibrational progressions associated with formation of the various ionic states has been completed, allowing confirmation of the symmetry and bonding characteristics of the four highest-energy occupied molecular orbitals of Cl 2 O.

Core shell excitation of 2-propenal (acrolein) at the O 1s and C 1s edges: An experimental and ab initio study

The carbon and oxygen K-shell spectra of gaseous 2-propenal (acrolein) have been measured using the inner-shell electron energy loss spectroscopy method. Large scale ab initio configuration interaction calculations have been carried out to enable firm assignments of the observed bands. The overall shapes of the spectra are similar to previous low resolution monolayer and multilayer phases NEXAFS spectra recorded by photoabsorption of synchrotron radiation, but the spectral bands are much better resolved than the earlier ones. The spectra are dominated by excitation of π* type states and by interaction between the C=C and C=O π* orbitals.

Core shell excitation of furan at the O1s and C1s edges: An experimental and ab initio study

The K-shell spectra of gaseous furan have been measured using the inner-shell electron energy loss spectroscopy (ISEELS) method at the carbon and oxygen thresholds. Large-scale ab initio configuration interaction calculations have been carried out in order to help in the assignments of the observed bands. The spectra are close to previous low resolution ones obtained using ISEELS in the gas phase and photoabsorption with the synchrotron radiation in gaseous and condensed phases. The presence of a new feature located at 287.3 eV in the C1s spectrum and recently detected by photoabsorption with synchrotron radiation is confirmed. At both edges, the calculations confirm the assignments proposed in earlier experimental works, with the exception of several C1s pre-edge features for which a new interpretation is given.

Re-analysis of the K-shell spectrum of benzene

Abstract The carbon K-shell spectrum of gaseous benzene has been recorded by inner-shell electron energy loss spectroscopy (ISEELS) under electric-dipole conditions (2 keV, small angle) with a resolution of 0.17 eV. Ab initio configuration interaction calculations performed in the frame of the equivalent core model have helped in the assignment of the experimental spectrum. They emphasize the importance of the multi-configurational approach and the role of the Rydberg orbitals in the assignment of some features. The band located at 289.09 eV is assigned to Rydberg excitations and a 3π* transition mixed with doubly excited configurations, and not to an anti-bonding (C–H) transition as suggested previously. Because of a large 3s/3d character of the (C–H)* orbital, the corresponding peak appears above the ionization threshold. The 293.8 eV band contains in-plane resonances and very likely also several doubly excited states with a 3π* contribution.

Electron and photon induced processes in SF5CF3

The photo-absorption cross section of trifluoromethyl sulphur pentafluoride, SF5CF3 has been measured using synchrotron radiation in the range of 4–11 eV (310nm>λ>110 nm) and comparison made with electron energy loss spectroscopy (EELS). The measured VUV cross sections are used to derive the photolysis rate of SF5CF3 in the terrestrial atmosphere. It is estimated that the lifetime for this molecule is the order of a 1000 years and the calculated global warming potential (GWP) is found to be between 17000 and 18100, making it one of the most potent global warming gases in the terrestrial atmosphere.

High resolution He I photoelectron spectrum of acrylonitrile

Abstract The photoelectron spectrum of acrylonitrile has been revisited under high resolution and high sensitivity using the He I resonance line. Ionisation of the outermost molecular orbitals is discussed in terms of ionisation energies and vibrational wavenumbers. Additional vibration features are reported.

Vibrational excitation of methane by 15 and 30 eV intermediate-energy electron impact

Absolute measurements of differential electron-collision cross sections have been performed for the vibrational excitation of methane in its electronic ground state at impact energies of 15 eV and, for the first time, at 30 eV, in the 8°–95° angular range. The normalization to the absolute scale has been carried out using the inelastic/elastic ratios and the absolute elastic differential cross section obtained from a relative flow technique recently developed in our laboratory, in which the elastic differential cross section of methane was compared to that of nitrogen at each impact energy and at each scattering angle. Special attention has been given to the small scattering angular range (⩽40°) where minima have been observed in the vibrational cross sections and where simultaneous independent measurements have been made on two different electron spectrometers.

Electronic excitation and oscillator strength of ethyl iodide by VUV photoabsorption and electron energy loss spectroscopy

A high resolution VUV photoabsorption spectrum of ethyl iodide has been recorded between 4 and 10.2 eV (310–120 nm) using synchrotron radiation. The spectrum consists of a broad structureless absorption band centered at 4.78 eV, followed by a region dominated by excitation of Rydberg states. A high resolution photoelectron spectrum (PES) of the lowest energy ionization band has been obtained and provides ionization energies necessary for identification of related Rydberg-excited states. Also, analysis of the vibrational fine structure in the PES has allowed identification of the normal vibrational modes excited and their wave numbers in the ion. These, in turn, have been used in the assignment of the lowest energy photoabsorption bands arising from electron excitation into the 6s Rydberg orbital. An electron energy loss spectrum has also been recorded from 5.8 to 14.2 eV, under electric-dipole conditions. It confirms the magnitude of the photoabsorption cross section values obtained using the synchrotron ...

Theoretical and experimental studies of the valence photoemission spectrum of propionitrile

Abstract The valence photoemission spectrum of propionitrile for all outer and inner valence levels up to the ionization energy of 23 eV is calculated by ab initio third-order algebraic diagrammatic construction (ADC(3)) Greens function method. The spectrum is also measured by high resolution He I photoelectron spectroscopy to resolve additional spectral features mainly due to the vibronic excitations. The present (ADC(3)) calculation provides a fairly good description of the vertical-electronic ionization spectral features of the valence PES spectrum of propionitrile. From the ionization threshold up to and including the 8a′ ionization, the ionization phenomena appear essentially as one-particle processes. For 11a′ and 10a′ ionization, the hole mixing occurs between this pair of ionization of the same symmetry, although the hole mixing is not so significant as in molecules containing several CN groups. For the innermost 7a′ band, the breakdown of the one-electron picture occurs.

MANY-ELECTRON EFFECTS IN THE VALENCE PHOTOEMISSION SPECTRUM OF 1,3,5,7-CYCLOOCTATETRAENE

Abstract The valence photoemission spectrum of 1,3,5,7-cyclooctatetraene (COT) has been calculated by an ab initio third order algebraic diagrammatic construction (ADC(3)) Greens function method and also measured by high resolution He I photoelectron spectroscopy. The major spectral features are well reproduced by the present many-body calculation. The additional spectral features observed at 10.054 and 12.757 eV cannot be predicted by either the ADC(3) or previous CI calculations, and are assigned to a Jahn-Teller distortion.