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See detailThe vacuum UV photoabsorption spectrum of methyl bromide (CH3Br) and its perdeuterated isotopomer CD3Br: a vibrational analysis
Locht, Robert ULg; Leyh, Bernard ULg; Dehareng, Dominique ULg et al

in Chemical Physics (2005), 317(1), 87-102

The fine structure of the vacuum UV photoabsorption spectrum of CH3Br and CD3Br has been analyzed in the 6.9-10.2 eV photon energy range. A large number of lines have been observed, classified and ... [more ▼]

The fine structure of the vacuum UV photoabsorption spectrum of CH3Br and CD3Br has been analyzed in the 6.9-10.2 eV photon energy range. A large number of lines have been observed, classified and assigned to the vibrational excitation accompanying a series of Rydberg transitions. The effects of the Jahn-Teller distortion and of the spin-orbit splitting of the ground electronic state of the ion have been considered. The former effect has been evaluated by ab initio calculations, showing that the E-2 state (in the C-3v symmetry group) splits into (2)A' and (2)A" states in the C-s symmetry group. Even though the energy difference of about 1 meV is extremely small, the (2)A' state is energetically the lowest component whereas the (2)A" is found to be a transition state. The Jahn-Teller stabilization energy and the wavenumbers associated with all vibrational modes have been calculated. Experimentally, the entire fine structure could be described in terms of three vibrational modes, i.e., hc omega(4) = 146 +/- 6 meV (1178 +/- 48 cm(-1)), hc omega(5) = 107 +/- 6 meV (863 +/- 48 cm(-1)) and hc omega(6) = 71 +/- 4 meV (572 +/- 32 cm(-1)), respectively, as resulting from an average over all analyzed Rydberg states. In CD3Br the corresponding energies are hc omega(4) = 104 +/- 3 meV (839 +/- 24 cm(-1)), hc omega(5)=82 +/- 4 meV (661 +/- 32 cm(-1)) and hc omega(6) = 62 +/- 4 meV (500 +/- 32 cm(-1)). These values are in fairly good agreement with those predicted by the present ab initio calculations for the ionic ground state. The experimental isotopic ratio rho(i) = [omega/omega(isot)](i) is 1.15 +/- 0.14, 1.31 +/- 0.14 and 1.39 +/- 1.0 and is predicted to be 1.04, 1.34 and 1.36, respectively, for omega(6), omega(5) and omega(4). On the basis of the present study an alternative assignment of the CH3Br+((X) over tilde E-2) photoelectron band structure is proposed. (C) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailThe vacuum Ultraviolet Photoabsorption and Photoelectron Spectroscopy of Fluoroethylenes. The 1,1-, cis- and trans-C2H2FCl.
Tornow, G.; Locht, Robert ULg; Kaufel, R. et al

in Chemical Physics (1990), 146

The vacuum ultraviolet absorption spectra of the three fluorochloroethene isomers were measured in the 6-13 eV photon energy range. Additionally, the HeI and NeI photoelectron spectra were recorded. The ... [more ▼]

The vacuum ultraviolet absorption spectra of the three fluorochloroethene isomers were measured in the 6-13 eV photon energy range. Additionally, the HeI and NeI photoelectron spectra were recorded. The assignment of the various photoelectron bands is based on MNDO calculations. The vaccum UV absorption spectral features were classified in terms of Rydberg series converging to the first and second ionization energy. Besides the typical pi-pi* transition, other valence transitions were observed and tentatively assigned. In the geminal isomer spectrum the dominant Rydberg series converge to the first ionization limit at 10.02 eV, in the cis and trans isomers the most intense Rydberg transitions converge to the second ionization energy at 11.87 and 12.03 eV respectively. The first ionization energies of these latter compounds, obtained by Rydberg series analysis, are 9.89 and 9.87 eV respectively. An assignment of the vibrational structure observed in both spectra is proposed. [less ▲]

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