M.-J. Hubin-Franskin

FRAGMENTATION OF METHYL CHLORIDE PHOTOEXCITED NEAR CL (2P) BY MASS SPECTROMETRY

The evolution of the fragmentation pathways of the methylchloride around the Cl 2p edge has been studied by use of charge separation mass spectrometry. Some fragmentation patterns are discussed in the frame of rapid fragmentation of the neutral and dissociation pathways characteristic of singly or multiply charged species. The correlation of the evolution of the charge separation spectra with the initial excitation process is used to give a definitive attribution to the pre‐edge features present in the absorption spectrum.

Electronic excitation and optical cross sections of methylamine and ethylamine in the UV-VUV spectral region

High resolution UV–VUV photon absorption spectra of methylamine and ethylamine have been recorded between 5.0–9.0 eV (250–140 nm) using synchrotron radiation. In methylamine, the energies of the absorption bands are confirmed as centered at 5.7, 7.2, and 8.7 eV, respectively. In ethylamine the band centers are 5.8, 7.0, and 7.9 eV, respectively; the last band is seen here for the first time. Most of the transitions exhibit rich fine structure dominated by vibrational progressions involving excitation of an amino wagging vibration. The absolute photoabsorption oscillator strengths have been measured by photon absorption over the 5–9 eV range and by dipolar electron energy loss spectroscopy from 5–14 eV (250–90 nm).

The core excitation of pyridine and pyridazine: An electron spectroscopy and ab initio study

The carbon and nitrogen K-shell excitation spectra of gaseous pyridine and pyridazine were recorded using the electron-energy loss spectroscopy under electric-dipole conditions (2 keV, small angle) with a resolution of 0.2 eV. Ab initio Configuration interaction calculations in the frame of the equivalent core model were performed in order to help in the assignment of the spectral features. The spectra are dominated by the transitions to the 1π* and σ* type orbitals. The C1s spectra of both molecules are close to that of benzene: The intensity of Rydberg transitions are enhanced by an important valence σC–H* character; the 1s→3π* transition is mixed with double excitations and give rise to several states, some of them lying above the ionization thresholds. Finally, the N1s spectra of both molecules are similar to the s-triazine one.

Morphologic and magnetic properties of Pd100−xFex nanoparticles prepared by ultrasound assisted electrochemistry

Nanopowdered alloys of Pd100−xFex, with x=4, 6, 8, and 12, have been prepared by ultrasound assisted electrochemistry. The composition of the individual particles, as determined by x-ray fluorescence, and the bulk composition, as determined by atomic absorption, are in agreement within experimental error. Transmission electron microscopy indicates that the nanopowders consist of agglomerates of small grains with a radius of approximately 5 nm, a radius which is confirmed by the broadening of the reflections in the x-ray powder diffraction patterns. X-ray fluorescence analysis of individual grains indicates a homogeneous distribution of palladium and iron throughout the grains. The x-ray diffraction patterns indicate that solid solutions of iron in palladium show no evidence of any pure palladium, any pure iron, or any other PdFe compound. The 78 K iron-57 Mossbauer spectra of these nanopowders reveal the presence of one magnetic sextet assigned to slowly relaxing superparamagnetic particles of Pd100−xFex ...

Electronic excitation of gaseous pyrrole and pyrazole by inner-shell electron energy loss spectroscopy

The spectroscopy of the unoccupied molecular orbitals of gaseous pyrrole and pyrazole has been studied by electron impact under electric dipole scattering conditions (2 KeV, small angle) and the inner-shell electron energy loss method. The core-excitation spectra have been recorded at the C1s and N1s edges with 0.2 eV resolution, resolution allowing to observe separately the transitions from the carbon atoms with different chemical environment. Ab initio calculations, using the equivalent core model, were performed to help in the interpretation of the spectral features. The spectra are dominated by transitions to the π* and σ* molecular orbitals. The calculations confirm that the 3b1(π*) orbital is the lowest-energy unoccupied one in pyrrole. In several cases, the intensity of the Rydberg excitations is enhanced by an important valence σ* character of the Rydberg orbitals.

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

Electronic state spectroscopy of limonene has been investigated using vacuum ultraviolet photoabsorption spectroscopy in the energy range 5.0-10.8 eV. The availability of a high resolution photon beam (~0.075 nm) enabled detailed analysis of the vibrational progressions and allowed us to propose, for the first time, new assignments for several Rydberg series. Excited states located in the 7.5-8.4 eV region have been studied for the first time. A He(I) photoelectron spectrum has also been recorded from 8.2 to 9.5 eV and compared to previous low resolution works. A new value of 8.521 ± 0.002 eV for the ground ionic state adiabatic ionisation energy is proposed. Absolute photoabsorption cross sections were derived in the 10-26 eV range from electron scattering data. All spectra presented in this paper represent the highest resolution data yet reported for limonene. These experiments are complemented by new ab initio calculations performed for the three most abundant conformational isomers of limonene, which we then used in the assignment of the spectral bands.

Inner-shell excitation of monocyanoethylene, trans-dicyanoethylene, and allylcyanide by electron energy loss spectroscopy

Inner-shell excitation spectra of gaseous monocyanoethylene, trans-dicyanoethylene, and allylcyanide have been measured at C1s and N1s edges using 2 keV electron collisions in quasi-dipolar excitation conditions and the electron energy loss spectroscopy. The energy resolution has allowed the observation of transitions from different carbon sites. Ab initio calculations have been made to help the assignment of the experimental features. The spectra below the core-electron ionization limit have been interpreted in terms of transitions to the lowest-energy valence unoccupied molecular orbitals shown to be of π* type in each molecule. The effects of the conjugation between the multiple bonds on the spectra and on the splitting of the π* type molecular orbitals have been discussed. Strong electronic relaxation effects have been evidenced.

Dissociation of the COS+ ion by photoionisation: experiment and ab initio calculations The A−X Franck-Condon energy gap an the A2Π, B2Σ+ vibronic state Franck-Condon energy regions

Abstract The predissociation or dissociation of selected vibronic levels of the X 2 Π, A 2 Π, and B 2 Σ + states of the COS+ ions has been studied experimentally. The product state distribution has been probed by photoabsorption of the synchrotron radiation in the 13.5–16.5 eV range and threshold photoelectron-photoion coincidence spectroscopy. Ab initio calculations have been performed to model the potential energy surfaces of the X 2 Π, A 2 Π, and B 2 Σ + electronic states and also of the lowest energy 4Σ− state. This latter is coupled by spin-orbit to X 2 Π and is confirmed to be responsible of the predissociation in the A − X Franck-Condon gap. In the A − X Franck-Condon energy gap the predissociation mechanism by 4Σ− is not statistical and favours the production of vibrationally excited CO (v″) with maximum probability for the highest energy accessible levels. It involves also a highly effective transfer into rotational motion. For the A 2 Π state, there is internal conversion to X 2 Π followed by predissociation to the lowest limit and, for the levels above the second limit, the predissociation by 4Σ− is in competition with direct dissociation of X 2 Π to the second limit. The B 2 Σ + state also undergoes internal conversion to X 2 Π followed by dissociation to the second limit and predissociation by 4Σ− to the first limit.

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.

Autoionization resonances in triatomic molecules

Review is made of the different types of information becoming available by the combined use of photoelectron spectroscopy and fluorescence excitation spectroscopy coupled to synchrotron radiation for the study of the dynamics of the triatomic molecules CO2, OCS and CS2. In particular, importance is layed on the decay pattern of the autoionization resonances associated with the valence shell excitations, their selectivity and possibly their coupling with dissociation.