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See detailThe Vacuum UV Photoabsorption Spectrum of the Geminal Dichloroethylene (1,1-C2H2Cl2) in the 5-20 eV Range. A Vibrational Analysis of the Valence and Rydberg States.
Locht, Robert ULiege; Dehareng, Dominique; Leyh, Bernard ULiege

in Journal of Physics Communications (2017), 1

The vacuum UV photoabsorption spectrum of 1,1-C2H2Cl2 is presented and discussed in detail in the 6 - 20 eV photon energy range. The broad band observed at 6.488 eV includes the 2b1()→σ*, 2b1()→ ... [more ▼]

The vacuum UV photoabsorption spectrum of 1,1-C2H2Cl2 is presented and discussed in detail in the 6 - 20 eV photon energy range. The broad band observed at 6.488 eV includes the 2b1()→σ*, 2b1()→* valence transitions and the 2b1()→3s Rydberg transitions. A quantum chemical calculation analysis is proposed and applied to the intertwined vibrational structure belonging to these transitions. For the →σ* and →* transitions short vibrational progressions are observed, analyzed and tentatively assigned. The →3s Rydberg transition is characterized by a single progression starting at 6.746 eV. The fine structure observed between 7.5 eV and 10.1 eV has been analyzed in terms of vibronic transitions to ns- (δ= 0.89), np- (δ= 0.59 and 0.37) and nd-type (δ= 0.16) Rydberg states all converging to the 1,1-C2H2Cl2+( 2B1) ionic ground state. The vibrational structure analysis excitation leads to the following wavenumbers: ω2≈ 1310 cm-1 (162 meV), ω4≈ 650 cm-1 (81 meV) and ω5≈ 290 cm-1 (37 meV). These modes can be assigned to the C=C stretching, to the symmetric C-Cl stretching and to the symmetric Cl-C-Cl bending vibrations respectively. By the same way, eight other Rydberg states were analyzed. For the first time the vacuum UV spectrum of 1,1-C2H2Cl2 has been recorded in the 10 eV-20 eV range, revealing intense broad bands which are assigned to transitions to Rydberg states converging to excited states of 1,1-C2H2Cl2+. Assignments are also proposed for the vibrational excitations observed in this range. [less ▲]

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See detailThe Photoelectron Spectroscopy of The Dichoroetylenes: The Geminal Isomer 1,1- Cl2C2H2. An Experimental and Quantum Chemical Study.
Locht, Robert ULiege; Dehareng, Dominique; Leyh, Bernard ULiege

in Journal of Physics Communications (2017), 1

This work analyzes the threshold photoelectron spectrum (TPES) and selected Constant Ion State (CIS) spectra of the 1,1-C2H2Cl2 isomer measured using synchrotron radiation. The TPES is compared to the HeI ... [more ▼]

This work analyzes the threshold photoelectron spectrum (TPES) and selected Constant Ion State (CIS) spectra of the 1,1-C2H2Cl2 isomer measured using synchrotron radiation. The TPES is compared to the HeI-, NeI- and ArII-photoelectron spectra (PES). In the HeI-PES nine photoelectron bands have been observed at vertical ionization energies of 9.992 eV, 11.652 eV, 12.157 eV, 12.536 eV, 13.633 eV, 14.195 eV, at about 15.9 eV and 16.2 eV and at 18.496 eV successively. For most of these bands the adiabatic ionization energy could be determined and a detailed vibrational analysis of the first four bands is presented. All these bands exhibit an extended vibrational structure. In particular, the ground electronic state and the third excited state display an extended vibrational structure upon excitation by the ArII-resonance line. The assignments of the electronic bands and of the vibrational structure are based on quantum chemical calculations. These allowed us to assign the nine electronic states in terms of ionization and double excitation in a molecular orbital scheme. The good correlation between predicted vibrational wavenumbers and the experimental values allowed us to assign all observed vibrational structures. The CIS spectrum of the eight first electronic states of 1,1-C2H2Cl2+ have also been recorded. Vibrationally resolved CIS spectra of the molecular ion ground state have been obtained and are discussed. [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 ULiege; Dehareng, Dominique ULiege; Leyh, Bernard ULiege

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

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

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

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 ULiege; Dehareng, Dominique ULiege; Leyh, Bernard ULiege

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 ULiege 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 detailThe Photoionization Dynamics of Methyl Iodide (CH3I): a joint Photoelectron and Mass Spectrometric Investigation.
Locht, Robert ULiege; Dehareng, Dominique ULiege; Hottmann, K. et al

in Journal of Physics : B Atomic Molecular & Optical Physics (2010), 43(10), 105101

The threshold photoelectron (TPES) and the photoionization mass spectrometric (PIMS) study of CH3I in the 8-20 eV photon energy range are presented. The interpretation and assignments are supported by ab ... [more ▼]

The threshold photoelectron (TPES) and the photoionization mass spectrometric (PIMS) study of CH3I in the 8-20 eV photon energy range are presented. The interpretation and assignments are supported by ab initio calculations. The TPES shows many new discrete features in the Jahn-Teller split ground X 2E (2A'-2A”) state of CH3I+. A new continuous band starting at about 11.7 eV is detected. These observations are essentially correlated with autoionizing transitions. This interpretation is supported by constant ion state (CIS) spectroscopy. A large enhancement of the transitions to the A 2A and B 2E ionic states is ascribed to large autoionizing contributions. Based on the present calculations, the weak to very weak bands in the 18.0 eV-23.0 eV photon energy range are mainly assigned to 2a1-1 ionization and to double excitations corresponding essentially to the 2e-2 4a11 and 3a1- 1 2e-1 4a11 configurations. The photoionization mass spectrometric study allowed us to investigate in detail the ionization and dissociation of CH3I+ leading to CH2+, CH3+, I+ and CH2I+ from the threshold up to 20 eV photon energy. The experimental data are compared to ab initio calculated dissociation energies. The threshold of appearance of CH3+, I+ and CH2I+ fragments are concentrated in the 12.2-12.7 eV photon energy range. All three exit channels are correlated with the ground state of CH3I+ via nonadiabatic transitions. All three fragment ions have to appear through predissociation of the ionic X 2E state and autoionizing dissociation from the (2E3/2)6p Rydberg state. This interpretation is strongly supported by the photoabsorption spectrum measured recently in the same photon energy range [1]. At higher energies, beside direct or predissociation of the A 2A1 and B 2E states of CH3I+, autoionization is also suggested to contribute to the fragmentation in all decay channels. [less ▲]

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See detailA Photoelectron Spectroscopic Investigation of Vinyl Fluoride (C2H3F). The HeI, Threshold and CIS Photoelectron Spectroscopy.
Locht, Robert ULiege; Leyh, Bernard ULiege; Dehareng, Dominique ULiege et al

in Journal of Physics : B Atomic Molecular & Optical Physics (2010), 43(1), 01510215

The threshold photoelectron spectrum (TPES) and the constant ion state (CIS) spectra of the individual ionic states of C2H3F have been recorded using synchrotron radiation. For comparison a well resolved ... [more ▼]

The threshold photoelectron spectrum (TPES) and the constant ion state (CIS) spectra of the individual ionic states of C2H3F have been recorded using synchrotron radiation. For comparison a well resolved HeI photoelectron spectrum (HeI-PES) has also been measured and analyzed in detail. The TPES has been measured between 9.5 eV and 35 eV photon energy. Numerous vibrational structures, reported for the first time, observed in the ground state and the six excited states of the cation are analyzed. Quantum chemical calculations have been performed and provide strong support to the assignments. State selected CIS spectra highlighted the major importance of autoionization for the production of almost all ionized states of C2H3F observed in this work. [less ▲]

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See detailThe Vacuum UV photoabsorption spectroscopy of Vinyl Fluoride (C2H3F): The vibrational fine structure and its analysis.
Locht, Robert ULiege; Leyh, Bernard ULiege; Dehareng, Dominique ULiege et al

in Chemical Physics (2009), 362(3), 97-108

The vacuum UV photoabsorption spectrum of C2H3F has been examined in detail between 6 eV and 25 eV photon energy by using synchrotron radiation. The analysis of the data is supported by ab initio quantum ... [more ▼]

The vacuum UV photoabsorption spectrum of C2H3F has been examined in detail between 6 eV and 25 eV photon energy by using synchrotron radiation. The analysis of the data is supported by ab initio quantum mechanical calculations applied to valence and Rydberg excited states of C2H3F. At 7.6 eV the pi-pi* and the 2a"->3s transitions are observed. An analysis is proposed and applied to the mixed fine structure belonging to these transitions. For the pi->pi* transition one single long vibrational progression is observed with hcwe= 95±7 meV (766±56 cm-1) and its adiabatic excitation energy is 6.892 eV (55 588 cm-1). The 2a"->3s transition is characterized by a single short progression with hc e= 167±10 meV (1 350±80 cm-1)starting at 6.974 eV (56 249 cm-1). From the present ab initio calculations these two wavenumbers best correspond to the vibrational modes v9 (CH2 rock in-plane, FCCbend) and v6 (CH2 rock in-plane, CF stretch) calculated at 615 cm-1 in the pi* state and 1 315 cm-1 in the (2A")3s Rydberg state respectively. The C=C stretching could not be excluded. The dense structured spectrum observed between 8.0 eV and 10.5 eV has been analyzed in terms of vibronic transitions to Rydberg states all converging to the C2H3F+(X2A") ionic ground state. An analysis of the associated complex fine structure of the individual Rydberg states has been attempted providing average values of the wavenumbers, e.g., for the (2A")3p Rydberg state hcw9= 60±1 meV (or 484±8 cm-1), hcw7= 151±7 meV (or 1 218±60 cm-1), hcw4= 191±3 meV (or 1 540±24 cm-1). The assignment of hcw= 105±5 meV (or 823±40 cm-1) is discussed. These experimental values are in good agreement with the theoretical predictions for C2H3F+ [R. Locht, B. Leyh, D. Dehareng, K. Hottmann, H. Baumgärtel, Chem.Phys. (in press)]. Above 10.5 eV and up to 25 eV several broad and strong bands are tentatively assigned to transitions to valence (V-V) and/or Rydberg (V-R) states converging to excited ionic states of C2H3F. [less ▲]

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See detailMedium and High Resolution Vacuum UV Photoabsorption Spectroscopy of Methyl Iodide (CH3I) and its deuterated isotopomers CD3I and CH2DI. A Rydberg series Analysis.
Locht, Robert ULiege; Leyh, Bernard ULiege; Jochims, H.-W. et al

in Chemical Physics (2009), 365(3), 109-128

The vacuum UV photoabsorption spectrum of CH3I has been investigated between 5 and 20 eV. Numerous vibronic transitions are observed. In the high 10-20 eV photon energy range weak to very weak diffuse ... [more ▼]

The vacuum UV photoabsorption spectrum of CH3I has been investigated between 5 and 20 eV. Numerous vibronic transitions are observed. In the high 10-20 eV photon energy range weak to very weak diffuse bands are observed and ascribed to electronic transitions from 3a1, 1e and 2a1 to Rydberg orbitals. In the 6-10.5 eV photon energy range more than 200 sharp and strong to weak lines have been observed. Several photon energy ranges were explored under high resolution conditions allowing us to observe many series up to high values of the principal quantum number n. They are assigned to vibrationless Rydberg transitions and classified into two groups converging to the two components of the spin-orbit split 2E state of CH3I+. These two groups consist of six different Rydberg series, i.e., nsa1, npa1, npe, nda1, nde and nf. A very close correlation has been established between the term values of the Rydberg states in CH3I and in Xe for ns, np, nd and nf Rydberg transitions. For the first time, the same measurements have been performed and the interpretation has been proposed for the photoabsorption spectrum of CH2DI and CD3I in the 6-10.5 eV photon energy range. For these two species, ionization energies are deduced: for the 2E3/2 and 2E1/2 states of CH2DI, these are IEad=9.544 eV and IEad=10.168 eV respectively and the corresponding energies are 9.552 eV and 10.173 eV in CD3I. [less ▲]

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See detailThe Role of Long-Range Forces in the Determination of Translational Kinetic Energy Release. Loss of C4H4+ from Benzene and Pyridine Cations.
Gridelet, E.; Locht, Robert ULiege; Lorquet, Andrée ULiege et al

in Journal of Physical Chemistry A (2008), 112

Kinetic energy release distributions (KERDs) for the benzene ion fragmenting into C4H4+ and C2H2 have been recorded by double-focussing mass spectrometry in the metastable energy window and by a retarding ... [more ▼]

Kinetic energy release distributions (KERDs) for the benzene ion fragmenting into C4H4+ and C2H2 have been recorded by double-focussing mass spectrometry in the metastable energy window and by a retarding field experiment up to an energy of 5 eV above the fragmentation threshold. They are compared with those resulting from the HCN loss reaction from the pyridine ion. Both reactions display a similar variation of the kinetic energy release as a function of the internal energy: the average release is smaller than statistically expected, with a further restriction of the phase-space sampling for the C5H5N+ dissociation. Ab initio calculations of the potential-energy profile have been carried out. They reveal a complicated reaction mechanism, the last step of which consists in the dissociation of a weakly bound ion-quadrupole or ion-dipole complex. The KERDs have been analyzed by the maximum entropy method. The fraction of phase-space effectively sampled by the pair of fragments has been determined and is similar for both dissociations. Both reactions are constrained by the square root of the released kinetic energy, epsilon1/2. This indicates that in the latter stage of the dissociation process, the reaction coordinate is adiabatically decoupled from the bath of the bound degrees of freedom. For the C6H6+ fragmentation, the analysis of the experimental results strongly suggests that, just as for the symmetric interaction potential, the translational motion is confined to a two-dimensional subspace. This dimensionality reduction of the translational phase space is due to the fact that the Hamiltonian of both weakly bound complexes contains a cyclic coordinate. [less ▲]

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See detailThe VUV Photoabsorption Spectroscopy and Photoionization of Halogenated Etylenes: Bromo-derivatives.
Locht, Robert ULiege; Leyh, Bernard ULiege; Jochims, H.-W. et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H - on CD-ROM (2006)

In this contribution the measurement, by the use of synchrotron radiation, of the V-UV photoabsorption spectrum (PAS) of 1,1-C2H2Br2 and the photoionization efficiency curve (PIC) of 1,1-C2H2Br2+ are ... [more ▼]

In this contribution the measurement, by the use of synchrotron radiation, of the V-UV photoabsorption spectrum (PAS) of 1,1-C2H2Br2 and the photoionization efficiency curve (PIC) of 1,1-C2H2Br2+ are reported. Strong correlations between the PAS and the PIC are shown. The PAS of 1,1-C2F2Br2 is also presented and compared to the PAS of 1,1-C2H2Br2 to show the influence of the fluuorine-substitution. [less ▲]

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See detailThe Photoabsorption and Photoionization of Bromine revisited.
Locht, Robert ULiege; Leyh, Bernard ULiege; Jochims, H.-W. et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlund m.b.H - on CD-ROM (2006)

The V-UV photoabsorption spectrum (PAS) and the photoionization (PIE) efficiency of Br2, Br2+ and Br+ have been measured using synchrotron radiation. At high photon energy a strong correlation between the ... [more ▼]

The V-UV photoabsorption spectrum (PAS) and the photoionization (PIE) efficiency of Br2, Br2+ and Br+ have been measured using synchrotron radiation. At high photon energy a strong correlation between the PAS of Br2 and the PIE of Br2+ is observed. A detailed analysis of the PIE of Br2+ in the threshold region is presented. New data related to the Br+/Br- ion-pair formation are reported. [less ▲]

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See detailHydrogen atom loss from the benzene cation. Why is the kinetic energy release so large?
Gridelet, E.; Lorquet, Andrée ULiege; Locht, Robert ULiege et al

in Journal of Physical Chemistry A (2006), 110(27), 8519-8527

The kinetic energy release distributions (KERDs) associated with the hydrogen loss from the benzene cation and the deuterium loss from the perdeuteriobenzene cation have been remeasured on the metastable ... [more ▼]

The kinetic energy release distributions (KERDs) associated with the hydrogen loss from the benzene cation and the deuterium loss from the perdeuteriobenzene cation have been remeasured on the metastable time scale and analyzed by the maximum entropy method. The experimental kinetic energy releases are larger than expected statistically, in contradistinction to what has been observed for the C-X fragmentations of the halogenobenzene cations. H(D) loss from C6H6+ (C6D6+) occurs via a conical intersection connecting the (2)A(2) and (2)A(1) electronic states. Two models are proposed to account for the experimental data: (i) a modified orbiting transition state theory (OTST) approach incorporating electronic nonadiabaticity; (ii) an electronically nonadiabatic version of the statistical adiabatic channel model ( SACM) of Quack and Troe. The latter approach is found to be preferable. It leads to the conclusion that the larger the energy stored in the transitional modes, which partly convert to the relative interfragment motion, the shorter the value of the reaction coordinate at which the adiabatic channels cross, and the larger the probability of undergoing the (2)A(2) -> (2)A(1) transition required for hydrogen loss. [less ▲]

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See detailAnalysis of kinetic energy release distributions by the maximum entropy method.
Leyh, Bernard ULiege; Gridelet, E.; Locht, Robert ULiege et al

in International Journal of Mass Spectrometry (2006), 249-250

Energy is not always fully randomized in an activated molecule because of the existence of dynamical constraints. An analysis of kinetic energy release distributions (KERDs) of dissociation fragments by ... [more ▼]

Energy is not always fully randomized in an activated molecule because of the existence of dynamical constraints. An analysis of kinetic energy release distributions (KERDs) of dissociation fragments by the maximum entropy method (MEM) provides information on the efficiency of the energy flow between the reaction coordinate and the remaining degrees of freedom during the fragmentation. For example, for barrierless cleavages, large translational energy releases are disfavoured while energy channeling into the rotational and vibrational degrees of freedom of the pair of fragments is increased with respect to a purely statistical partitioning. Hydrogen atom loss reactions provide an exception to this propensity rule. An ergodicity index, F, can be derived. It represents an upper bound to the ratio between two volumes of phase space: that effectively explored during the reaction and that in principle available at the internal energy E. The function F(E) has been found to initially decrease and to level off at high internal energies. For an atom loss reaction, the orbiting transition state version of phase space theory (OTST) is especially valid for low internal energies, low total angular momentum, large reduced mass of the pair of fragments, large rotational constant of the fragment ion, and large polarizability of the released atom. For barrierless dissociations, the major constraint that results from conservation of angular momentum is a propensity to confine the translational motion to a two-dimensional space. For high rotational quantum numbers, the influence of conservation of angular momentum cannot be separated from effects resulting from the curvature of the reaction path. The nonlinear relationship between the average translational energy <epsilon > and the internal energy E is determined by the density of vibrational-rotational states of the pair of fragments and also by non-statistical effects related to the incompleteness of phase space exploration. The MEM analysis of experimental KERDs suggests that many simple reactions can be described by the reaction path Hamiltonian (RPH) model and provides a criterion for the validity of this method. Chemically oriented problems can also be solved by this approach. A few examples are discussed: determination of branching ratios between competitive channels, reactions involving a reverse activation barrier, nonadiabatic mechanisms, and isolated state decay. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailAbout the Photoionization of Methyl Bromide (CH3Br). Photoelectron and Photoionization Mass Spectrometric Investigation.
Locht, Robert ULiege; Leyh, Bernard ULiege; Dehareng, Dominique ULiege et al

in Chemical Physics (2006), 323

The threshold photoelectron (TPES) and the photoionization mass spectrometric (PIMS) study of CH3Br in the 8-20 eV photon energy range is presented. The interpretation and assignments are supported by ab ... [more ▼]

The threshold photoelectron (TPES) and the photoionization mass spectrometric (PIMS) study of CH3Br in the 8-20 eV photon energy range is presented. The interpretation and assignments are supported by ab initio calculations. The TPES shows several new discrete features in the Jahn-Teller split ground state X2E(2A'-2A") of CH3Br+. An additional continuous band starts at about 11.8 eV. These observations are both correlated with direct ionization and autoionizing transitions. This is supported by constant ion state (CIS) spectroscopy. A large enhancement of the transitions to the A2A and B2E states is ascribed to important autoionizing contributions. Based on the present calculations, the weak to very weak bands in the 17.5-22.0 eV photon energy range were mainly assigned to 2a1 ionization and to double excitations described essentially by the 2e-24a11 and 1e-12e-14a11 configurations. The photoionization mass spectrometric study allows us to investigate in detail the ionization and dissociation of CH3Br+ leading to CH2+, CH3+, Br+ and CH2Br+ from threshold up to 20 eV photon energy. The experimental data are compared to ab initio dissociation energies. At the onset, the CH3+ and CH2Br+ fragment ion production is correlated with the ground state of CH3Br+ and both fragment ions have to appear through dissociative autoionization from the (3a11/1e1)6s or 5s Rydberg state. This interpretation is supported by the photoabsorption spectrum measured recently in the same photon energy range. At higher energies, beside a likely direct (pre)dissociation of the A2A1 and B2E states of CH3Br+, autoionization also contributes to the fragmentation in all decay channels. Avoided crossings in a manyfold of 2A' states are likely to be involved. This is supported by ab initio calculations. For CH3+ the photoion-pair process is analyzed and detailed assignments are proposed on the basis of our latest VUV photoabsorption spectroscopic data. [less ▲]

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See detailThe vacuum UV photoabsorption spectrum of methyl bromide (CH3Br) and its perdeuterated isotopomer CD3Br: a Rydberg series analysis
Locht, Robert ULiege; Leyh, Bernard ULiege; Jochims, H.-W. et al

in Chemical Physics (2005), 317(1), 73-86

The vacuum UV photoabsorption spectrum of CH3Br has been recorded between 6 and 25 eV. A large number of vibronic bands are observed. They were partly ascribed to vibrationless Rydberg transitions. In the ... [more ▼]

The vacuum UV photoabsorption spectrum of CH3Br has been recorded between 6 and 25 eV. A large number of vibronic bands are observed. They were partly ascribed to vibrationless Rydberg transitions. In the high photon energy range of 12-25 eV, very weak diffuse bands are mostly assigned to transitions from the 3a(1), 1e and (2a(1) + 1a(1)) to 3s orbitals. In the 6-12 eV photon energy range, numerous weak to strong bands are observed. The sharpness is very variable over the entire spectral region. In a first step, the interpretation of the spectrum and the assignment of the Rydberg transitions is based on the simple Rydberg formula. The observed features are classified in two groups of four series, each converging to one of the two spin-orbit components of the (X) over tilde E-2 state of CH3Br+. Rydberg series of nsa(1), npa(1), npe, nd and possibly nf characters are observed. The same measurements have been made for the first time on CD3Br in the 6-12 eV photon energy range. The observed features are classified into the same Rydberg series characterized by nearly the same delta values. Ionization energies for CD3Br (X) over tilde (2) E-3/2 at 10.565 eV and (X) over tilde (2) E-1/2 at 10.902 eV are deduced. In a second step, we fitted the experimental data to an energy expression taking into account both the exchange interaction and the spin-orbit coupling. Already states with n = 6 are found to correspond to Hund's case (c). Constant values of the quantum defects are deduced. (C) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailThe Photoabsorption and Photoionization of Halogenated Ethylenes: brominated Derivatives.
Locht, Robert ULiege; Leyh, Bernard ULiege; Jochims, H.-W. et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H - on CD-ROM (2005)

The V-UV photoabsorption spectrum of C2HBrF2, C2BrF3 and C2ClF3 have been measured using synchrotron radiation. The mass spectrometric photoionization of C2HBrF2 is also reported.

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