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See detailThe Photoionization Dynamics of Methyl Iodide (CH3I): a joint Photoelectron and Mass Spectrometric Investigation.
Locht, Robert ULg; Dehareng, Dominique ULg; 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 ULg; Leyh, Bernard ULg; Dehareng, Dominique ULg 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 ULg; Leyh, Bernard ULg; Dehareng, Dominique ULg 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 ULg; Leyh, Bernard ULg; 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 VUV Photoabsorption Spectroscopy and Photoionization of Halogenated Etylenes: Bromo-derivatives.
Locht, Robert ULg; Leyh, Bernard ULg; 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 ULg; Leyh, Bernard ULg; 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 detailAbout the Photoionization of Methyl Bromide (CH3Br). Photoelectron and Photoionization Mass Spectrometric Investigation.
Locht, Robert ULg; Leyh, Bernard ULg; Dehareng, Dominique ULg 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 ULg; Leyh, Bernard ULg; 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 ULg; Leyh, Bernard ULg; 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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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 Photoionization Mass Spectrometric Study of the Three membered Ring Systems C3H6, C2H4O and C2H4S and their open Chain Isomers.
Locht, Robert ULg; Leyh, Bernard ULg; Jochims, H.-W. et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H - on CD-ROM (2004)

The dissociative photoionization mass spectrometric study of C2H6, C2H4O and C2H4S has been measured using synchrotron radiation. The ionization efficiency curves of the molecular ions of the three ... [more ▼]

The dissociative photoionization mass spectrometric study of C2H6, C2H4O and C2H4S has been measured using synchrotron radiation. The ionization efficiency curves of the molecular ions of the three species are reported. [less ▲]

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See detailThe Vacuum UV Photoabsorption Spectroscopy of the Three membered Ring Systems C3H6, C2H4O and C2H4S and their open Chain Isomers.
Locht, Robert ULg; Leyh, Bernard ULg; Jochims, H.-W. et al

Book published by Berliner Elektronen Speicherring für Elektronen Synchrotron Strahlung m.b.H - on CD-ROM (2004)

The vacuum UV photoabsorption spectrum of C3H6, C2H4O and C2H4S have been measured using synchrotron radiation and are reported.

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See detailPhotoabsorption Spectroscopy at medium Resolution. The C2HXYZ (XYZ= H, F, Cl and/or Br) Molecules.
Locht, Robert ULg; Leyh, Bernard ULg; Jochims, H.-W. et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H - on CD-ROM (2003)

The V-UV photoabsorption spectra of 1,1-C2H2F2, C2HBrF2 and C2HClF2 have been recorded by using synchrotron radiation and are reported.

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See detailHigh Resolution Photoabsorption Spectroscopy of CH3Br, CH3I and their Isotopomers.
Locht, Robert ULg; Leyh, Bernard ULg; Jochims, H.-W. et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H - sur CD-ROM (2002)

Several spectral regions in the Vacuum UV have been recorde under high resolution conditions: i.e. 8.185-8.210 eV (2e->5pa1 Rydberg transition) in CH(D)3Br and 7.300-7.325 eV in CH(D)3I (2e->6pa1 Rydberg ... [more ▼]

Several spectral regions in the Vacuum UV have been recorde under high resolution conditions: i.e. 8.185-8.210 eV (2e->5pa1 Rydberg transition) in CH(D)3Br and 7.300-7.325 eV in CH(D)3I (2e->6pa1 Rydberg transition). These spectra were recorded with 50µeV resolution. Structures separated by 100-150 µeV are observed and are shown to be isotope dependent. [less ▲]

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See detailHigh Resolution Photoabsorption Spectroscopy of the three Methyl Halides. Tests and first Results.
Locht, Robert ULg; Jochims, H.-W.; Baumgärtel, H.

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H - on CD-ROM (2002)

The photoaborption spectrum of the monohalogenated methanes has been remeasured by using a new 3m-NIM monochromator under high resolution conditions. Many structures in the 10 eV photon energy range are ... [more ▼]

The photoaborption spectrum of the monohalogenated methanes has been remeasured by using a new 3m-NIM monochromator under high resolution conditions. Many structures in the 10 eV photon energy range are very well resolved and compared with previous very high resolution data. [less ▲]

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See detailThe Vacuum UV Photoabsorption Spectrum of Methyl Chloride (CH3Cl) and its perdeuterated Isotopomer CD3Cl. I. A Rydberg Series Analysis.
Locht, Robert ULg; Leyh, Bernard ULg; Hoxha, A. et al

in Chemical Physics (2001), 272

The vacuum UV photoabsorption spectrum of CH3Cl has been recorded between 6 and 25 eV. A large number of vibronic bands are observed. These were partly ascribed to vibrationless Rydberg transitions. In ... [more ▼]

The vacuum UV photoabsorption spectrum of CH3Cl has been recorded between 6 and 25 eV. A large number of vibronic bands are observed. These were partly ascribed to vibrationless Rydberg transitions. In the higher energy range of 12-25 eV very weak diffuse bands are mostly assigned to transitions from the 3a1, 1e and 2a1 to 3s orbitals. In the 6-12 eV photon energy range, numerous weak to strong bands are observed. The sharpness of the features 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 X2E state of CH3Cl+. Rydberg series of nsa1 (delta=1.069 and 1.064), npa1 (delta= 0.68 and 0.66), npe (delta= 0.438 and 0.427) and nd (delta= -0.040 and -0.092) characters are observed. The same measurements have been made for the first time on CD3Cl in the 6-12 eV photon energy range. The same Rydberg transitions are observed. Analogous series are characterized by about the same delta values: nsa1 (delta= 1.038 and 0.968), npa1 (delta= 0.65 and 0.61), npe (delta= 0.458 and 0.462) and nd (delta= -0.004 and -0.082). Ionization energies for CD3Cl X2E3/2 at 11.320 eV and X2E1/2 at 11.346 eV are deduced. In a second step, we fitted the experimental data for the nsa1 and npa1 states to an energy expression taking into account both the exchange interaction and the spin-orbit coupling. This accounts for the progressive switching from Hund's case (a) to Hund's case (c). [less ▲]

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See detailAbout the Photoionization of Methyl Chloride. A Threshold Photoelectron Spectroscopic and Photoionization Mass Spectrometric investigation.
Locht, Robert ULg; Leyh, Bernard ULg; Hoxha, A. et al

in Chemical Physics (2001), 272

The threshold photoelectron spectroscopic (TPES) and the photoionization mass spectrometric (PIMS) study of Methyl Chloride (CH3Cl) in the 8-20 eV photon energy is presented. The interpretation and ... [more ▼]

The threshold photoelectron spectroscopic (TPES) and the photoionization mass spectrometric (PIMS) study of Methyl Chloride (CH3Cl) in the 8-20 eV photon energy is presented. The interpretation and assignments are supported by ab initio calculations. The detailed analysis of the TPES shows numerous features in the Jahn-Teller split ground X2E(2A'-2A") state of CH3Cl+ and a new continuus band peaking at 13.4 eV. These were assigned to both direct ionization and autoionizing transitions. The transitions to the A2A1 and to the B2E states undergo a large enhancement ascribed to important autoionizing contributions. Based on the present calculations, the weak to very weak signals in the 19-26 eV photon energy range were mainly assigned to 2a1-1 ionization and to double excitations described essentially by 2e-2, 4a11 and 1e-1, 2e-1, 4a11 configurations. The PIMS study allowed us to investigate in detail the ionization and dissociation of CH3Cl+ into CH2+, CH3+, CHCl+ and CH2Cl+ from threshold up to 20 eV photon energy. At the onset, the CH3+, CHCl+ and CH2Cl+ fragment ion production is correlated to the ground state of CH3Cl+ and all fragment ions have to appear through dissociative autoionization from the 2e->3p Rydberg state. This interpretation is supported by the photoabsorption spectrum (PAS) measured recently in the same photon energy range. At higher energies, beside direct dissociation of the A2A1 and B2E states of CH3Cl+ autoionization also contributes to the fragmentation in all decay channels. For CH3+ the photoion-pair process is analyzed and detailed assignments are proposed on the basis of recent PAS data. [less ▲]

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See detailThe Vacuum UV Photoabsorption spectrum of Methyl Chloride (CH3Cl) and its perdeuterated Isotopomer CD3Cl. II. A vibrational Analysis.
Locht, Robert ULg; Leyh, Bernard ULg; Hoxha, A. et al

in Chemical Physics (2001), 272

The fine structure of the vacuum UV photoabsorption spectrum of CH3Cl and CD3Cl has been analyzed in the 7.5-10.5 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 CH3Cl and CD3Cl has been analyzed in the 7.5-10.5 eV photon energy range. A large number of lines have been observed, classified and assigned to vibrational excitation accompanying a series of Rydberg transitions. The vibronic transitions involve both Jahn-Teller distortion and spin-orbit splitting. The former effect has been evaluated by ab initio calculations showing that the 2E state (in the C3v symmetry group) splits into 2A' and 2A" states in the Cs symmetry group. The 2A' state is energetically the lowest component whereas the 2A" is found to be a transition state. The Jahn-Teller stabilisation energy and the wavenumbers associated with all vibrational modes have been calculated. Experimentally, the entire fine structure could be described by using the vibrational modes, i.e. hcomega5= 104+/-7 meV, hcomega6= 77+/-7 meV and homega=162+/-3 meV respectively, as resulting from an average over all the analyzed Rydberg states. In CD3Cl the corresponding energies are hcomega5= 81+/-4 meV, hcomega6= 66+/-5 meV and hcomega= 124+/-4 meV. These values are in good agreement with those predicted by the present ab initio calculations for the ion ground state. However, the agreement is not so good for the wavenumber omega which could be assigned to the nu3 or nu4 vibrational modes. Though some arguments favour nu4 (the CH3 umbrella mode), within the error limits on the present measurements it is formally not possible to ascribe this wavenumber to one of these two vibrations. [less ▲]

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See detailThe photoabsorption and Constant Ion State Spectroscopy of Vinyl Bromide.
Hoxha, A.; Locht, Robert ULg; Leyh, Bernard ULg et al

in Chemical Physics (2000), 260

In this paper we report the photoabsorption and the constant ion state spectroscopy of vinyl bromide (C2H3Br). The photoabsorption spectrum was measured using synchrotron radiation and was investigated in ... [more ▼]

In this paper we report the photoabsorption and the constant ion state spectroscopy of vinyl bromide (C2H3Br). The photoabsorption spectrum was measured using synchrotron radiation and was investigated in detail between 5.0 and 12.0 eV photon energy revealing many previously unobserved structures. These features were analyzed in terms of valence to virtual valence transitions and Rydberg series. The examination of the three Rydberg series converging towards the first ionization threshold (2a"->ns, 2a"->np and 2a"->nd) leads to wavenumbers of 335+/-30, 690+/-30 and 1305+/-30 cm-1. The vibrational wavenumbers of the progressions belonging to Rydberg series converging towards the second ionization threshold are 485+/-30 and 1145+/-50 cm-1. Ab initio calculations helped the assignment of the valence transitions and of the observed vibrational wave numbers in the Rydberg series. Constant Ionic State spectra were recorded for vibronic states corresponding to the first and the second electronic states of the ion. Their fine structures are assigned to the autoionization of Rydberg states. The autoionization decay of these Rydberg states is analyzed qualitatively in terms of the vibrational nature of the final ionic state. [less ▲]

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See detailAbout the Vacuum UV Photoabsorption Spectrum of Methyl Fluoride (CH3F): the fine structure and its vibrational analysis.
Locht, Robert ULg; Leyh, Bernard ULg; Hoxha, A. et al

in Chemical Physics (2000), 257

The vacuum UV photoabsorption spectrum of CH3F has been recorded between 7 and 24 eV and has been analyzed in detail. Broad and structureless peaks are observed over the entire photon energy range. They ... [more ▼]

The vacuum UV photoabsorption spectrum of CH3F has been recorded between 7 and 24 eV and has been analyzed in detail. Broad and structureless peaks are observed over the entire photon energy range. They are all assigned to transitions to Rydberg states, members of series converging to the 2e-1, 5a-1 and 1e-1 ionization limits. These features are underlying very long series of narrow and weak structures in the range of 10-13.2 eV. Through a continuum subtraction procedure, about 70 lines could clearly be identified. These have been assigned to long vibrational progressions belonging to Rydberg states corresponding to the 2e->3p and 2e->6s/5d configurations. These states are split by a Jahn-Teller distortion. Ab initio calculations lead to a Jahn-Teller stabilization energy of about 0.84 eV. The main features observed in the two bands are assigned to one single long vibrational progression of hcomega=0.160 eV (1290cm-1) related to the C-F Jahn-Teller inactive stretching vibration. The remaining structure is assigned to the low excitation of the Jahn-Teller active vibrational modes, i.e. the bending modes nu5 and nu6 characterized by hcomega5=0.120 eV (970 cm-1) and hcomega6=0.082 eV (660 cm-1). Leaning on the present results and assignments previously reported photoelectron spectroscopic data on CH3F+ [L. Karlsson, R. Jadrny, L. Mattsson, F.T. Chau, K. Siegbahn Phys.Scripta 16 (1977) 225] have been reconsidered and reinterpreted. [less ▲]

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