Marie-Jeanne Hubin-Franskin

Intramolecular dynamics by photoelectron spectroscopy. I. Application to N+2, HBr+, and HCN+

The 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 10−13 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 Xu20092Σ+g, ...

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.

2-methyl furan: An experimental study of the excited electronic levels by electron energy loss spectroscopy, vacuum ultraviolet photoabsorption, and photoelectron spectroscopy

The vacuum ultraviolet absorption spectrum of 2-methyl furan has been recorded between 5 eV (248 nm) and 9.91 eV (125 nm) and absolute photoabsorption cross sections measured. The electronic excited states of the molecule have also been probed using high resolution electron energy loss spectroscopy. Recorded under electric-dipole conditions, it has confirmed the magnitude of the photoabsorption cross section values and extended the optical oscillator strength values up to 12 eV. Measurements at several scattering angles have allowed the angular behavior of differential cross section ratios for some features in the 5-7.1 eV region to be measured, which in turn have helped in the assignments of electronic states to observed absorption bands. A high-resolution photoelectron spectrum was measured and allowed the two lowest ionization energies to be determined, these have been used in the identification of the related Rydberg states. Vibrational fine structure in the photoelectron spectrum has also been analyzed. The spectrum is dominated by intense pi-pi(*) transitions. Rydberg series associated with the first and second ionization energies have been identified. The effects of symmetry reduction induced on the furan ring by the methyl substitution are also discussed

VUV optical-absorption and near-threshold electron energy-loss spectra of pyrazole

Abstract The gas-phase VUV absorption spectrum of pyrazole between 5 and 11 eV (250–110 nm) is reported, for the first time. The spectrum is diffuse, but is unusual because of the presence of a window resonance at about 7.8 eV, ascribed to interaction of a Rydberg state with an underlying valence continuum. A related near-threshold electron energy-loss spectrum reveals low-lying triplet states ( 3 ππ * ) at about 3.9 and 5.1 eV, respectively, and anionic states (electron/molecule resonances) having electron attachment energies of about 0.75, 2 and 6.5 eV, respectively. The UV-photoelectron He(I) spectrum has been re-measured with improved energy-resolution.

Vibrational excitation of methylamine by electron impact in the 4.5–30 eV energy range

Vibrational excitation of gaseous methylamine induced by 4.5–30 eV energy electrons has been investigated by the electron energy loss spectroscopy. The ratios of the differential cross sections for excitation of the vibrational modes and for elastic scattering measured as a function of the electron kinetic energies show that at 15 and 30 eV, the vibrational excitation occurs mainly through a direct mechanism. The absolute vibrationally elastic and inelastic differential cross sections have been measured at these impact energies. The cross sections for the inelastic scattering are strongly dependent on the vibrational mode which is excited.

Dissociative Ionization of Carbon Disulphide in the Gas Phase. Heat of Formation of the CS Radical.

Abstract Measurements of the appearance potentials and the kinetic energies of S + and CS + ions formed by electron impact on carbon disulphide in the gas phase lead us to propose a value as low as 34 ± 6 kcal mole −1 for the heat of formation of the CS radical in its ground electronic state. It is also shown that the predissociations of the A 2 Π u /or X 2 Π g and the B 2 Σ u + molecular ion states by a repulsive 4 Σ − state giving rise to S + ions, observed through metastable ions study, occur at 13.45 eV and 14.55 eV respectively.

Electronic and vibrational excitation of acrylonitrile by low and intermediate energy electrons

Electronic and vibrational excitation of acrylonitrile induced by 3–50 eV energy electrons has been investigated by the electron energy loss spectroscopy. Electronic excitation spectra have been recorded for 30 and 50 eV impact energies at a 10° scattering angle in the energy loss range from 5.5 to 11.5 eV, corresponding to the excitation of electrons belonging to the outermost‐valence‐shell molecular orbitals. We have reviewed the assignment of the valence excited states occurring in the 5.5–9 eV energy loss region. The vibrational patterns associated with the two lowest‐energy singlet valence excited states have also been re‐examined. Moreover, we have proceeded for the first time to the analysis and attribution of several Rydberg series converging to the ionic ground state and to its two lowest‐energy electronic excited states. The study of the excitation function of the C—H stretching modes of acrylonitrile in the 3–11 eV electron impact energy range has shown evidence of a broad shape resonance built...

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.

Lowest energy triplet states of furan, studied by high resolution electron energy loss spectroscopy

Abstract The excitation spectrum of furan has been recorded between 3 and 6.2 eV by high resolution electron energy loss spectroscopy at 30 eV incident electron energy and scattering angles of 10° and 25°. The lowest energy singlet–triplet transitions are confirmed to be responsible for two bands centred at 3.97 eV ( 3 B 2 ) and 5.15 eV ( 3 A 1 ), respectively. Vibrational structure is resolved for the first time in the 3 A 1 band and its analysis has provided identification of the excited state normal modes and their energy.

Electronic States of Tetrahydrofurfuryl Alcohol (THFA) As Studied by VUV Spectroscopy and Ab Initio Calculations

The electronic spectroscopy of isolated tetrahydrofurfuryl alcohol (THFA) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 5.0-10.8 eV energy-range, with absolute cross-section measurements derived. The He(I) photoelectron spectrum was also collected to quantify ionization energies in the 9-16 eV spectral region. These experiments are supported by the first high-level ab initio calculations performed on the excited states of the neutral molecule and on the ground and excited state of the positive ion. The good agreement between the theoretical results and the measurements allows us to quantify for the first time the electronic-state spectroscopy of THFA. The present work also considers the question of the lowest energy conformers of the molecule and its population distribution at room temperature.