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See detailThe threshold photoelectron spectroscopy of the cis- and trans-1-chloro-2-fluoro-ethene isomers. An experimental and quantum chemical study.
Locht, Robert ULg; Dehareng, Dominique ULg; Leyh, Bernard ULg

in Journal of Physics : B Atomic Molecular & Optical Physics (2014), 47(17), 175101-175012

The threshold photoelectron spectra (TPES) of the two vicinal isomers of the 1,2-C2H2FCl molecule have been investigated in the 9-24 eV energy range using synchrotron radiation. Eight (for the cis-isomer ... [more ▼]

The threshold photoelectron spectra (TPES) of the two vicinal isomers of the 1,2-C2H2FCl molecule have been investigated in the 9-24 eV energy range using synchrotron radiation. Eight (for the cis-isomer) or nine (for the trans-isomer) bands have been observed and the corresponding ionization energies have been determined. The spectroscopic assignments are based on high level quantum chemical ab initio calculations for both isomers. Most of the observed spectral features could be interpreted. For both species the first three TPES bands exhibit a rich vibrational structure. Vibrational energies were determined and assignments were also supported by quantum chemical calculations of vibrational wavenumbers for these three ionic states of both isomers. [less ▲]

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See detailVibronic Valence and Rydberg Transitions in Geminal Chloro-Fluoro-Ethene (1,1-C2H2FCl). A Spectroscopic and Quantum Chemical Investigation.
Locht, Robert ULg; Dehareng, Dominique ULg; Leyh, Bernard ULg

in Molecular Physics (2014), 112(11), 1520-1539

The vacuum UV photoabsorption spectrum of 1,1-C2H2FCl has been examined in detail between 5 eV and 15 eV photon energy by using synchrotron radiation dispersed by three different monochromators. Quantum ... [more ▼]

The vacuum UV photoabsorption spectrum of 1,1-C2H2FCl has been examined in detail between 5 eV and 15 eV photon energy by using synchrotron radiation dispersed by three different monochromators. Quantum chemical calculations are performed to help in the analysis of the valence/Rydberg transitions region centered at 7.05 eV including the 3a”(pi)→pi* and the 3a” (pi*)→3s Rydberg transitions. Interactions between states involving transitions to the 3s, 4d and sigma* orbitals are identified. A vibrational analysis is proposed for the structures belonging to these transitions. For the pi(3a”)→pi* transition, one vibrational progression is observed with ω3=1410±50 cm-1 and its lowest excitation energy is determined at about 6.398±0.003 eV. The pi(3a”)→3s Rydberg transition is characterized by a single progression with ω3= 1410±80 cm-1 likely starting at about 6.45 eV. These vibrations are ascribed to the C=C stretching motion. The abundant structure observed in the spectrum between 7.8 eV and 10.5 eV has been analyzed in terms of vibronic transitions to ns (δ= 0.97), np (δ= 0.63 and 0.40) and nd (δ= 0.13 and -0.11) Rydberg states which belong to series converging to the 1,1-C2H2FCl+( 2A”) ionic ground state. The analysis of the vibrational structure of the individual Rydberg states has been attempted leading to average values of the wavenumbers ω3= 1 420±20 cm-1, ω7= 720±50 cm-1 and ω9= 390±50 cm-1. Between 10.5 eV and 12.5 eV nine other Rydberg states converging to the 1,1-C2H2FCl+ ( 2A') first excited state were analyzed by the same way. The vibrational structure of these Rydberg states results from the excitation of one vibrational normal mode ν7 with an average value of ω7= 520±20 cm-1 which is assigned to the C-Cl stretching vibration as inferred from quantum chemical calculations. [less ▲]

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See detailThe Threshold Photoelectron Spectrum of Geminal Chloro-Fluoro-ethene (1,1-C2H2FCl) isomer. Experiment and Theory.
Locht, Robert ULg; Dehareng, Dominique ULg; Leyh, Bernard ULg

in Journal of Physics : B Atomic Molecular & Optical Physics (2014), 47(8), 0851019

The threshold photoelectron spectrum (TPES) of 1,1-C2H2FCl has been measured for the first time using synchrotron radiation. It has been compared to the HeI photoelectron spectrum (PES) obtained earlier ... [more ▼]

The threshold photoelectron spectrum (TPES) of 1,1-C2H2FCl has been measured for the first time using synchrotron radiation. It has been compared to the HeI photoelectron spectrum (PES) obtained earlier [Tornow G. et al., Chem.Phys. 146 115 (1990)]. Eight photoelectron bands have been observed at 10.22 eV, 12.45 eV, 13.28 eV, 14.29 eV, 14.99 eV, 17.12 eV, 17.67 eV, and at 20.23 eV successively. Only the first three bands exhibit a rich and extensive vibrational structure. Their adiabatic ionization energies are measured and a detailed vibrational analysis is presented. The assignments of the electronic bands and of the vibrational wavenumbers were made by using ab initio quantum chemical calculations. These allowed us to provide the MO description of the eight electronic states in terms of ionization and double excitation. The good correlation between predicted vibrational wavenumbers and the experimental values provides a strong basis for the assignment of all the vibrational structures. [less ▲]

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See detailMetallo-supramolecular micellar gels: a structural study
Mugemana, Clément; Joset, Arnaud ULg; Guillet, Pierre et al

Poster (2013, July 10)

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See detailMetallo-supramolecular micellar gels: a structural study
Mugemana, Clément; Joset, Arnaud ULg; Guillet, Pierre et al

Conference (2013, May 17)

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See detailIon Dissociation Kinetics in Mass Spectrometry
Leyh, Bernard ULg

in Reedijk, J. (Ed.) Reference Module in Chemistry, Molecular Sciences and Chemical Engineering (2013)

The variation of fragmentation rate constants as a function of the parent ion internal energy, or, alternatively, as a function of temperature, is crucial information to unravel the dissociation ... [more ▼]

The variation of fragmentation rate constants as a function of the parent ion internal energy, or, alternatively, as a function of temperature, is crucial information to unravel the dissociation mechanisms of molecular ions. This contribution provides the reader first with basic information on the statistical theories used to model unimolecular rate constants. Various experimental methods to measure such rate constants in the 102 to 1010 s^(-1) range are then discussed. Kinetic isotope effects are also briefly dealt with. How reaction mechanisms can be inferred from kinetic data is handled in an extensive section where selected examples from the recent literature are discussed. [less ▲]

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See detailThe Vacuum UV photoabsorption spectroscopy of the geminal ethylene difluoride (1,1-C2H2F2). The vibrational structure and its analysis.
Locht, Robert ULg; Jochims, H.W.; Leyh, Bernard ULg

in Chemical Physics (2012), 405

The vacuum UV photoabsorption spectrum of 1,1-C2H2F2 has been examined in detail between 6 eV and 25 eV photon energy by using synchrotron radiation. The broad band observed at 7.52 eV includes the →∗ and ... [more ▼]

The vacuum UV photoabsorption spectrum of 1,1-C2H2F2 has been examined in detail between 6 eV and 25 eV photon energy by using synchrotron radiation. The broad band observed at 7.52 eV includes the →∗ and the 2b1→3s Rydberg transitions. An analysis is proposed and applied to the fine structure belonging to these transitions. For the (2b1)→∗ transition, one long vibrational progression is observed with ω2=1 475±80 cm-1 combined with one quantum of vibration of ω4= 976±24 cm-1 and its adiabatic excitation energy is determined at 6.742 eV. The 2b1→3s Rydberg transition is characterized by a single progression with ω2=1532±80 cm-1 starting at 6.957 eV. These vibrations are ascribed to the C=C and C-F stretching motions respectively. The abundant structure observed between 8.2 eV and 11.2 eV has been analyzed in terms of vibronic transitions to ns (δ= 0.98) and two different np (δ= 0.50 and 0.31) and nd (δ= 0.13 and 0.044) Rydberg series all converging to the 1,1-C2H2F2+(B1) ionic ground state. An analysis of the associated vibrational structure of the individual Rydberg states has been attempted providing average values of the wavenumbers ω2= 1 549±16 cm-1, ω4= 839±40 cm-1 and ω5= 589±16 cm-1. Eight other Rydberg states were also analyzed. The vacuum UV spectrum of 1,1-C2H2F2 has been recorded for the first time above 11.2 eV and up to 25 eV. Several broad and strong bands are tentatively assigned to transitions to Rydberg states which are members of Rydberg series converging to excited ionic states of 1,1-C2H2F2. For several of these Rydberg states vibrational, structures are observed and assignments are proposed. [less ▲]

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See detailThe Spectroscopy of the Geminal Ethylene difluoride (1,1-C2H2F2): HeI, threshold and Constant Ion State spectroscopies.
Locht, Robert ULg; Dehareng, Dominique ULg; Leyh, Bernard ULg

in Journal of Physics : B Atomic Molecular & Optical Physics (2012), 45(11), 115101

The threshold photoelectron spectrum (TPES) and the constant ion state (CIS) spectra of the individual ionic states of 1,1-C2H2F2 have been recorded using synchrotron radiation. The TPES has been measured ... [more ▼]

The threshold photoelectron spectrum (TPES) and the constant ion state (CIS) spectra of the individual ionic states of 1,1-C2H2F2 have been recorded using synchrotron radiation. The TPES has been measured between 9.5 eV and 28 eV photon energy. For comparison the HeI photoelectron spectrum (HeI-PES) has also been measured and analyzed in detail. Numerous vibrational structures, reported for the first time, observed in the ground state and the seven excited states of the cation are analyzed. Quantum chemical calculations have been performed and provided support to the assignments. The exceptional contribution of autoionization to the HeI PES could be emphasized. State selected CIS spectra highlighted the importance of the autoionizing contribution to the production of almost all ionized states of 1,1-C2H2F2 observed in this work. Several peculiarities of the vibrationally resolved CIS spectra are analyzed. [less ▲]

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See detailA photoionization mass spectrometric and threshold photoelectron-photoion coincidence study of vinylbromide (C2H3Br) in the vacuum ultraviolet range of 6-21 eV.
Hoxha, A.; Yu, S.-Y.; Locht, Robert ULg et al

in Chemical Physics (2011), 379(1-3), 99-108

The dissociative photoionization of vinyl bromide (C2H3Br) has been investigated by photoionization mass spectrometry (PIMS) and time-of-flight threshold photoelectron-photoion coincidence (TOF-TPEPICO ... [more ▼]

The dissociative photoionization of vinyl bromide (C2H3Br) has been investigated by photoionization mass spectrometry (PIMS) and time-of-flight threshold photoelectron-photoion coincidence (TOF-TPEPICO) spectrometry using synchrotron radiation. The photoionization efficiency curves of the three most abundant ions, i.e. C2H3Br+, C2H3+ and C2H2+, are measured and analyzed in detail. A C2H3+/Br- photoion-pair formation process has been detected for the first time. Some arguments are provided in favor of the electronic excitation of the C2H3+ fragment and of the isomerization of the C2H2+ ions. The breakdown diagram for these ions in the 9.8–21 eV photon energy range, derived from TOF-TPEPICO mass spectra, is discussed. The involvement of the successive C2H3Br+ ionic states and the role of autoionization of C2H3Br Rydberg states are emphasized. For the two minor HBr+ and Br+ fragment ions only the breakdown diagrams are measured and appearance energies are derived. [less ▲]

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See detailGas Phase Fullerene Anions Hydrogenation by Methanol Followed by IRMPA Dehydrogenation
Greisch, Jean-François ULg; Leyh, Bernard ULg; Remacle, Françoise ULg et al

in Journal of the American Society for Mass Spectrometry (2010), 21(1), 117-126

The characterization in the gas phase of the mechanisms responsible for hydride formation can <br />contribute to the development of new materials for hydrogen storage. The present work <br />provides ... [more ▼]

The characterization in the gas phase of the mechanisms responsible for hydride formation can <br />contribute to the development of new materials for hydrogen storage. The present work <br />provides evidence of a hydrogenation-dehydrogenation catalytic cycle for C60 anions in the <br />gas phase using methanol vapor at room temperature as hydrogen donor. [less ▲]

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