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See detailThe elementary reactions of energy selected 1,1-Difluoroethene ions.
Güthe, F.; Weitzel, K.-M.; Baumgärtel, H. et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H (1996)

The dissociative photoionization dynamics of 1,1-difluoroethene has been investigated by TPEPICO using synchrotron radiation. The breakdown diagram has been build. The attention has been focussed on C2HF ... [more ▼]

The dissociative photoionization dynamics of 1,1-difluoroethene has been investigated by TPEPICO using synchrotron radiation. The breakdown diagram has been build. The attention has been focussed on C2HF+ (HF-loss) channel. [less ▲]

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See detailReactivity and Collisionally Activated Dichlorocarbene Dications studied by Tandem Mass Spectrometry.
Leyh, Bernard ULg; Hautot, D.

in Journal of the American Society for Mass Spectrometry (1995), 6

The dissociation mechanisms of dichlorocarbene dications following collisional activation have been investigated via tandem mass spectrometric technique and semi-empirical calculations. Three channels ... [more ▼]

The dissociation mechanisms of dichlorocarbene dications following collisional activation have been investigated via tandem mass spectrometric technique and semi-empirical calculations. Three channels appear to be significant: (CCl2)2+->CCl+(X1Sigma+)+Cl+(3P) (channel 1); (CCl2)2+->CCl+(X1Sigma+)+Cl+(1D) (channel 2); (CCl2)2+->(Cl2)+(X2Pig)+C+(2P). The second channel becomes dominant at high internal energy. Production of ground state fragments (channel 1) involves a transition driven by spin-orbit coupling from the (CCl2)2+ X 1Sigma+g state to the (CCl2)2+ a 3Sigma-u state en route to the fragments. The dissociation barrier for the production of the ground state fragments from the ground electronic state of (CCl2)2+ via the spin-orbit-induced transition is equal to 420 kJ/mol. The dissociation pathway that corresponds to channel 3 includes a first isomerization step from the linear (Cl-C-Cl)2+ structure to a bent (Cl-C-Cl)2+ connectivity. The calculated isomerization barrier amounts to 550 kJ/mol. The calculated reverse activation barriers are compatible with the measured kinetic energy released on the fragments. [less ▲]

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See detailReaction Window in the single-electron capture by Ammonia Dications.
Leyh, Bernard ULg; Hoxha, Antuan

in Chemical Physics (1995), 192

Single-electron capture (SEC) by (NH3)2+ with rare gases (He, Ne, Ar, Kr, Xe) and benzene, (NH3)2++G->NH3++G+, has been investigated using a forward geometry double-focussing mass spectrometer. The SEC ... [more ▼]

Single-electron capture (SEC) by (NH3)2+ with rare gases (He, Ne, Ar, Kr, Xe) and benzene, (NH3)2++G->NH3++G+, has been investigated using a forward geometry double-focussing mass spectrometer. The SEC cross-section goes through a maximum within a reaction window centered at an exothermicity of approximately 4.5 eV. This corresponds to a target-projectile distance for the charge transfer of about 3.2 Angstöm. The average internal energy of NH3+-ions resulting from SEC has been obtained both via translational energy gain measurements and via an analysis of the daughter ion spectra. The agreement between both methods is satisfactory and shows that the lower the ionisation energy of the target, the more probable the excitation of NH3+ to the A2E state. With benzene (ionization energy=9.25 eV) as the target gas, however, the excess energy is converted partly to internal energy of C6H6+, leading most probably to the D2B2u, E2B1u and F2A1g states of C6H6+. A model based on the Landau-Zener non-adiabatic formalism, including one entrance channel (NH32++G) and two exit channels (NH3+ X2A"2+G+ and NH3+ A2E+G+) accounts qualitatively for the observed results in the case of exothermic single-electron capture. This model is not appropriate for slightly exothermic and endothermic charge transfer, i.e., in the present case, for the Ne and He target gases. [less ▲]

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See detailPhotoionization Dynamics of Mono- and Difluoroethylenes.
Leyh, Bernard ULg; Locht, Robert ULg; Hottmann, K. et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H (1995)

Using synchrotron radiation, the threshold photoelectron spectrum and vibrationally resolved CIS-spectra have been recorded between 10-28 eV photon energy for C2H3F and 1,1-C2H2F2.

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See detailResonant Autoionization in Vinylchloride between 10-12 eV.
Locht, Robert ULg; Leyh, Bernard ULg; Hottmann, K. et al

Book published by Berliner Elektronen Speischerring für Synchrotron Strahlung m.b.H (1995)

The threshold photoelectron spectrum of Vinylchloride has been recorded using synchrotron radiation. The attention is focussed on the abundant fine structure between 10-12 eV and has been assigned to ... [more ▼]

The threshold photoelectron spectrum of Vinylchloride has been recorded using synchrotron radiation. The attention is focussed on the abundant fine structure between 10-12 eV and has been assigned to vibrational autoinization. [less ▲]

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See detailChemical Reactions in the Cluster Ions of 1,1-Difluoroethene and Argon.
Güthe, F.; Jochims, H.-W.; Leyh, Bernard ULg et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H (1995)

The preparation conditions of 1,1-difluoroethene-Ar clusters has been investigated by photoionization using synchrotron radiation. The nature of the products has been identified by a quadrupole mass ... [more ▼]

The preparation conditions of 1,1-difluoroethene-Ar clusters has been investigated by photoionization using synchrotron radiation. The nature of the products has been identified by a quadrupole mass spectrometer. [less ▲]

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See detailReaction Dynamics of Collisionally activated Ammonia Cations.
Leyh, Bernard ULg; Hoxha, A.

in Chemical Physics (1994), 179

In the framework of a research on the collisional mechanisms involved in tandem mass spectrometry, the collisional activation processes of NH3+ with different target gases have been investigated. The ... [more ▼]

In the framework of a research on the collisional mechanisms involved in tandem mass spectrometry, the collisional activation processes of NH3+ with different target gases have been investigated. The experiments have been performed on an upgraded AEI-MS9 sector instrument equipped with two collision cells and include daughter ion spectra, ion kinetic energy spectra, determination of kinetic energy release distributions (KERD) and appearance energy measurements. We have shown that collisionally activated dissociation (CAD) of NH3+ into NH++[H,H] depends upon the internal energy of NH3+. This internal energy effect is also observed for the NH2++H channel, when Xe is the target gas; with He, such an effect could not be detected. The analysis of the KERD shows that production of NH2+ upon CAD takes place from the NH3+ ground electronic state by rotational predissociation; two components are observed, one which corresponds to a near-threshold process (mean kinetic energy release <T>=0.13 eV), and one characterized by <T>=0.56 ev corresponding to an excess energy of 2.1 eV above the dissociation threshold. NH+ fragments can be formed by two processes: the first one occurs at threshold and leads to NH+(X2Pi)+H2(X1Sigma+g); the second one is characterized by large KER values (up to 7 eV) and leads to either electronically excited NH+ or dissociation of H2. [less ▲]

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See detailReaction Dynamics of the Dichlorocarbene Anion Using tandem Mass Spectrometry.
Leyh, Bernard ULg; Mélon, Pierre

in Organic Mass Spectrometry (1993), 28

The dissociation dynamics of CCl2- anions were studied under various internal energy conditions. This study involved the measurement of daughter-ion spectra and branching ratios and of the amount of ... [more ▼]

The dissociation dynamics of CCl2- anions were studied under various internal energy conditions. This study involved the measurement of daughter-ion spectra and branching ratios and of the amount of kinetic energy released (KER) on the fragments. The competition between C and Cl loss for CCl2- ions created by many of the following sequence of processes: CCl4->CCl2+->(G=Xe, Kr C6H6)->CCl2--> fragments (1); CCl4->(CCl2--+[Cl,Cl]+;CCl2-; CCl2- (Ne)-> Fragments (2); CCl4->(CCl2)2+ (C6H6)->CCl2--> fragments (3) was particularly investigated. For process (1), the amount of fragmentating CCl2- ions is 8-10 times larger with Kr than with Xe or C6H6. The KER for Cl loss is smaller than 0.20 eV with the three target gases used. For the loss of C, the KER is much larger (0.7 eV). This KER is, however, equal to 0.21 eV for the collisionally activated C loss in process (2). For this latter process, the C loss vs Cl loss branching ratio decreases with increasing internal energy. The KERs measured for process (3) are vary similar to those obtained for process (1). It is suggested that repulsive or slightly bound excited states which correlate directly to the Cl2-(X2Sigma+)+C asymptote and which are vibronically coupled to the ground state play an important role in these dissociation processes. [less ▲]

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See detailUnimolecular reaction dynamics from Kinetic Energy Release Distributions. 1 - Dissociation of Bromobenzene Ions.
Lorquet, Jean-Claude ULg; Leyh, Bernard ULg

in Organic Mass Spectrometry (1993), 28

Preliminary data on a new method for extracting data from the kinetic energy release distribution of metastable fragment ions are presented. This method can give information concerning the energy ... [more ▼]

Preliminary data on a new method for extracting data from the kinetic energy release distribution of metastable fragment ions are presented. This method can give information concerning the energy threshold of the reaction and the energy dependence of the rate constant (i.e. its logarithmic derivative). It was applied to bromine loss from bromobenzene cations. [less ▲]

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See detailIon Translational Energy Distributions from Inner-shell Dissociative ionization of N2O, NH3 and SF6.
Locht, Robert ULg; Leyh, Bernard ULg; Jochims, H. W. et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H (1992)

The IRPD method is applied to the dissociative ionization in the inner-shell ionization region for NO+, N2+, O+, N+ and N++/N2O. Particular attention has been focussed on the production and ion kientic ... [more ▼]

The IRPD method is applied to the dissociative ionization in the inner-shell ionization region for NO+, N2+, O+, N+ and N++/N2O. Particular attention has been focussed on the production and ion kientic energy distribution of H+/NH3. [less ▲]

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See detailPhotoionization of NH3 and its Isotopomers between 10 and 12 eV.
Locht, Robert ULg; Leyh, Bernard ULg; Denzer, W. et al

in Kistemaker, P. G.; Nibbering, N. M. (Eds.) Advances in Mass Spectrometry: Proceedings of the 12th IMSC, Amsterdam (International Mass Spectrometry Conference 26-30 August 1991): Book of Abstracts. (1991)

The photoionization of NH3 and its isotopomers is measured between 10-12 eV photon energy by using synchrotron radiation. The abundant autoionization structure observed in the ionization efficiency curves ... [more ▼]

The photoionization of NH3 and its isotopomers is measured between 10-12 eV photon energy by using synchrotron radiation. The abundant autoionization structure observed in the ionization efficiency curves is analyzed. [less ▲]

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See detailVibrational Autoionization in NH3 and its Isotopomers in the 10-12 eV photon energy range.
Locht, Robert ULg; Leyh, Bernard ULg; Denzer, W. et al

in McCarthy, I. E.; MacGillivray, W. R.; Weigold, E. (Eds.) et al 17th International Conference on the Physics of Electronic and Atomic Collisions. Book of Abstracts. (1991)

The observation and detailed analysis of the vibrational autoionization in NH3 and its three isotopomers is reported.

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See detailVibrational Autoionization in NH3 and its Isotopomers in the 10-12 eV photon energy range.
Locht, Robert ULg; Leyh, Bernard ULg; Denzer, W. et al

in MacGillivray, W. R.; McCarthy, I. E.; Standage, M. C. (Eds.) ICPEAC Abstracts (International Conference on the Physics of Electronic and Atomic Collisions) (1991)

The photoionization efficiency curves of the four isotopomers of NH3 have been recorded using synchrotron radiation. The abundant fine structure has been interpreted in terms of vibrational structure of ... [more ▼]

The photoionization efficiency curves of the four isotopomers of NH3 have been recorded using synchrotron radiation. The abundant fine structure has been interpreted in terms of vibrational structure of Ryberg series which autoionize. [less ▲]

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See detailThe Photoionization of Ammonia revisited. The Vibrational Autoionization of NH3 and its three Isotopomers in the 10-12 eV photon energy range.
Locht, Robert ULg; Leyh, Bernard ULg; Denzer, W. et al

in Chemical Physics (1991), 155

The photoionzation efficiency curves of NH3 and its three isotopomers have been investigated in the photon energy range of the first ionized state. From the analysis of the corresponding vibrational ... [more ▼]

The photoionzation efficiency curves of NH3 and its three isotopomers have been investigated in the photon energy range of the first ionized state. From the analysis of the corresponding vibrational structure, wavenumbers and anharmonicity constants are deduced. The detailed investigation of the abundant autoionization structure tends to show the adiabatic ionization energy to be 10.072+/-0.010 eV for NH3, NH2D and NHD2 and 10.083+/-0.010 eV for ND3. All autoionization features were classified in vibrational progressions (nu2 bending mode) belonging to nasa1 (or nd) and npe (n=5, 6, 7) Rydberg series. Vibrational autoionization occurs through Delta v transitions up to -9. A qualitative analysis of the intensity distribution of these series strongly supports that transitions involving odd Delta v values are favoured. This observation can be understood by applying group theoretical considerations to the theory of vibrational autoionization. [less ▲]

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See detailInfluence of Electronic Excitation in the Charge Reversal of halogenated Cations.
Leyh, Bernard ULg; Wankenne, H.

in International Journal of Mass Spectrometry and Ion Processes (1991), 107

Charge reversal of high kinetic energy (8keV) cations during collisions with atomic target gases (G=Xe, Kr, Ne) has been studied for CCln+ (n=1 or 2) ions resulting from dissociative electroionization of ... [more ▼]

Charge reversal of high kinetic energy (8keV) cations during collisions with atomic target gases (G=Xe, Kr, Ne) has been studied for CCln+ (n=1 or 2) ions resulting from dissociative electroionization of CCl4. The influence of electronic excitation of the incident cation CCln+ and of the nature of the target gas G on the anion yield have been examined. In our experiments, the two-collision process CCln+->CCln+G+->(CCln-)+2G+ is predominant. By comparing the anion and cation yields as a function of the kinetic energy of the ionizing electrons, we found evidence, with some target gases, of the existence of long-lived excited states of CCl+ and CCl2+, which lead to an increase in the anion yield in comparison with charge reversal of the correponding ground state ions. For CCl+, we deduce an excitation energy of 4+/-1 eV with a lifetime longer than 6.2 µs. These results are compatible with the a3Pi long-lived state of CCl+ previously detected by optical spectroscopy and by charge-stripping experiments. Our experimental data on charge reversal and metastable dissociation of CCl2+ reveal the existence of a long-lived state (lifetime>8.2 µs) of CCl2+ lying at 4.3+/-1 eV above the ground state.Semi-empirical MNDO calculations show that the energy of the first quartet state, a4A2, is compatible with the observed excitation energy. The spin-orbit coupling-induced transition from the a4A2 state to the B2A2 state is suggested to play an important role in the metestable dissociation CCl2+*->(CCl+)+Cl. The origin of the increase in the anion yield when long-lived excited states of CCl+ and CCl2+ are charge-reversed is discussed. Step a is suggested to be responsible for this yield enhancement which is observed when an appropriate target gas makes this step quasi-resonant. [less ▲]

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See detailThe isomerization of oxirane. Stable .CH2OCH2., .CH2CH2O. and :CHOCH3 and Their Counterpart Ions
Wesdemiotis, Chrysostomos; Leyh, Bernard ULg; Fura, Aberra et al

in Journal of the American Chemical Society (1990), 112

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See detailThe Photoionization of Ammonia Revisited. The Autoionization in NH3 and its three Isotopomers in the 10-12 eV photon energy range.
Locht, Robert ULg; Leyh, Bernard ULg; Denzer, W. et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H (1990)

The photoionization efficiency curves of NH3, NH2D, NHD2 and ND3 have been measured using synchrotron radiation. The fine structure has been interpreted in terms of vibrational autoionization.

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See detailCouplings between Normal Modes studied by the Correlation Function. Duschinsky Effect and Fermi Resonance.
Pavlov-Verevkin, V. B.; Leyh, Bernard ULg; Lorquet, Jean-Claude ULg

in Chemical Physics (1989), 132

The dynamical information contained in a correlation function obtained by the Fourier transform of an electronic spectrum can be used to study strong intermode couplings, such as the Duschinsky effect (DE ... [more ▼]

The dynamical information contained in a correlation function obtained by the Fourier transform of an electronic spectrum can be used to study strong intermode couplings, such as the Duschinsky effect (DE) and the Fermi resonance (FR). Both of them complicate the calculation of the correlation function by destroying its factorisability. In some particular cases, the DE can greatly simplify the form of the correlation function by concealing one of its inherent frequencies. The DE never leads to a beat or to a systematic decrease of the correlation function. A simple classical approximation for the correlation function which takes into account the Lissajous motion of the center of the wave packet, but does not allow for its deformation or spreading is found to be useful in a harmonic model. The FR leads to a beat in the correlation function which results from a periodic energy transfer from the active to the inactive mode. A practical method is given to extract the perturbed and unperturbed energies as well as the coupling matrix element of a FR from a low-resolution spectrum by Fourier transformation of just that part of the spectrum which corresponds to the quasidegenerate interacting states. The case of the B2Sigma+u state of CS2+ is treated as an example. [less ▲]

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See detailComplex structures in the calculated photoionization spectrum of CO in the 17-17.5 eV energy region.
Leyh, Bernard ULg; Raseev, Gheorghe

in Journal of Chemical Physics (1988), 89(2), 820-829

Complicated spectral features appear in the CO photoionization spectra between 17 and 17.5 eV photon energy. In order to interpret these processes, we refine in the present paper our previous model [B ... [more ▼]

Complicated spectral features appear in the CO photoionization spectra between 17 and 17.5 eV photon energy. In order to interpret these processes, we refine in the present paper our previous model [B. Leyh and G. Raseev, Phys.Rev. A34, 2920 (1986)] by introducing all the vibrational levels of the first three electronic states of CO+. This more accurate treatment leads to two major results. The resonance at 17.1 eV and 17.3 eV are complex resonances resulting from the interaction between the Rydberg series converging to the A2Pi and B2Sigma+ ionic states: they can no more be assigned simply to Rydberg states converging to CO+ B2Sigma+. The intermediate experimental feature at 17.2 eV, missing in our previous calculation, is now present in the theoretical spectrum. Mainly, this feature, which we have called composite resonance, is a broadned (by the experimental resolution) superposition of Rydberg states converging to the A2Pi,v+=4 state. In this paper, we present and analyze the vibrationally resolved cross sections and symmetry parameter for the X2Sigma+,v+=0-3 and A2Pi,v+0-4 states. These theoretical results are compared to recent experimental data by Leyh et al. [Chem.Phys.115, 243 (1987)] and by Hardis and co-workers (the preceeding paper). [less ▲]

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See detailElectronic Autoionization in Carbon monoxide: The effects of the Vibrational Motion.
Leyh, Bernard ULg; Delwiche, Jacques ULg; Hubin-Franskin, Marie-Jeanne ULg et al

in Chemical Physics (1987), 115

New continuous measurements of the vibrationally resolved photoionization cross sections of CO+ X2Sigma+ and A2Pi between 63 and 83 nm are reported. We assign the Rydberg series converging to CO+ A2Pi ... [more ▼]

New continuous measurements of the vibrationally resolved photoionization cross sections of CO+ X2Sigma+ and A2Pi between 63 and 83 nm are reported. We assign the Rydberg series converging to CO+ A2Pi. The effects of the vibrational motion are interpreted on the basis of the Condon approximation. This approximation is shown to allow a qualitative understanding of the decay of the Rydberg series converging to the A2Pi and B2Sigma+ states of CO+. [less ▲]

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