References of "Leyh, Bernard"
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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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See detailTheoretical Study of Electronic Autoionization in CO: Vibrationally resolved results between 17 and 18.3 eV.
Leyh, Bernard ULg; Raseev, G.

in Physical Review. A : General Physics (1986), 34(4), 2920-2935

We have theoretically studied the electronic autoionization between 17 and 18.3 eV of Rydberg series converging to the B 2Sigma+ state of CO+ (RB series). We have obtained partial and vibrationally ... [more ▼]

We have theoretically studied the electronic autoionization between 17 and 18.3 eV of Rydberg series converging to the B 2Sigma+ state of CO+ (RB series). We have obtained partial and vibrationally resolved differential and total photoionization cross sections by combining ab initio electronic quantities with a variant of the two-step multichannel quantum defect theory (MQDT). The formalism of the Feshbach projection operators is used to separate the electronic quantities needed in the first and second steps of the MQDT. We have introduced the vibrational motion within the Condon approximation. Our results lead to new unambiguous assignments of the RB series. The vibrationally resolved cross sections, the associated branching ratios, and the background and resonant features are discussed in detail and compared with the available experimental data. There is an overall agreement between theory and experiement except for the angular distribution of photoelectrons. [less ▲]

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See detailAutoionization in Diatomic Molecules: an example of Electrostatic Autoionization in CO.
Raseev, G.; Leyh, Bernard ULg; Lefebvre-Brion, H.

in Zeitschrift für Physik. D, Atoms, Molecules, and Clusters (1986), 2

A review is presented of the different types of autoionization which have been studied theoretically in diatomic molecules: electronic (or electrostatic), rotational, spin-orbit and vibrational ... [more ▼]

A review is presented of the different types of autoionization which have been studied theoretically in diatomic molecules: electronic (or electrostatic), rotational, spin-orbit and vibrational autoionizations. An example involving a large number of vibrational channels is treated. It concerns the electrostatic autoionization in the 730-708 Angstöm wavelength region which appears in the CO photoionization spectrum. The structure observed at 721 Angstrôm is explained by the enhancement in intensity of numerous levels of Rydberg series converging to excited levels of the A 2Pi state caused by two autoionized Rydberg levels with a B 2Sigma+ core. [less ▲]

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See detailMeasured and Calculated Partial Photoionization Cross Sections of CO between 15 and 40 eV.
Leyh, Bernard ULg; Raseev, G.; Hubin-Franskin, Marie-Jeanne ULg et al

in Lahmani, F.; Castex, M. C.; Collin, Jacques (Eds.) et al Photophysics and Photochemistry above 6 eV. (1985)

Vibrationally resolved partial photoionization cross sections of CO have been measured and theoretical partial cross sections have been calculated using the method of Raseev et al. and the two-step MQDT ... [more ▼]

Vibrationally resolved partial photoionization cross sections of CO have been measured and theoretical partial cross sections have been calculated using the method of Raseev et al. and the two-step MQDT formulation of Giusti-Suzor and Lefebvre-Brion. We discuss the physical nature of the shape resonances appearing in the epsilon-sigma continua and we analyze their vibrational selectivity. A new assignment of the Rydberg series converging to CO+(B2Sigma+) is suggested and their electronic and vibrational selectivity is discussed. [less ▲]

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See detailPotential Energy Surfaces and Theory of Unimolecular Dissociation.
Lorquet, Jean-Claude ULg; Leyh, Bernard ULg

in Almoster Ferreira, M. A. (Ed.) Ionic Processes in the Gas Phase. (1984)

Reaction mechanisms can be determined from ab initio calculations of potential energy surfaces. Their complicated nature explains the frequent success of statistical theories, but non-statistical ... [more ▼]

Reaction mechanisms can be determined from ab initio calculations of potential energy surfaces. Their complicated nature explains the frequent success of statistical theories, but non-statistical behaviour is also accounted for. A certain correlation between structure and reactivity can be established, subject to many qualifications. Information on the nuclear motion on the potential energy surfaces of an ionized molecule can be extracted from a photoelectron spectrum by a Fourier transform operation. [less ▲]

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See detailIntramolecular Dynamics of Molecular Ions.
Lorquet, Jean-Claude ULg; Lorquet, Andrée ULg; Dehareng, Dominique ULg et al

in Bulletin de la Société Chimique Belge (1983), 92(6/7), 609-611

The Fourier transform of an electronic spectrum gives a direct dynamic information on the nuclear motion of a wavepacket on the potential energy surface of the final state reached in the electronic ... [more ▼]

The Fourier transform of an electronic spectrum gives a direct dynamic information on the nuclear motion of a wavepacket on the potential energy surface of the final state reached in the electronic transition, at least during the first few molecular vibrations. The method is valid for both adiabatic and non-adiabatic situations. It has proved its usefulness in the study of molecular processes such as Duchinsky effect, fast predissociations and internal conversions. [less ▲]

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See detailLineweaver-Burk, Hanes, Eadie-Hofstee and Dixon Plots in Non-steady-state Situations.
Frère, Jean-Marie ULg; Leyh, Bernard ULg; Renard, André

in Journal of Theoretical Biology (1983), 101

Lineweaver-Burk, Hanes, Eadie-Hofstee and Dixon plots can only be used when a true initial rate is measured. Despite the fact that this point has often been stressed, it is far too often ignored in favour ... [more ▼]

Lineweaver-Burk, Hanes, Eadie-Hofstee and Dixon plots can only be used when a true initial rate is measured. Despite the fact that this point has often been stressed, it is far too often ignored in favour of restricting the essay time to one where low amounts of substrate are used. When one or several irreversible and slow steps occur with an inactivator during the incubation of a ternary enzyme-substrate-inactivator mixture, the rate of the enzyme-catalyzed reaction progressively decreases. Even under these conditions, the present computer simulations investigations show that apparently linear Lineweaver-Burk, Hanes, Eadie-Hofstee and Dixon graphs can be obtained when the amount of product is mistakenly assumed to represent the true initial rate. Moreover, the observed pattern can change with time, going for instance from non-competitive to competitive. "Ki's" measured under these conditions also vary with time and bear little relationship to the true constants involved in the interaction. [less ▲]

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See detailIntramolecular dynamics by photoelectron spectroscopy. II. Nonadiabatic processes.
Dehareng, Dominique ULg; Leyh, Bernard ULg; Desouter-Lecomte, Michèle ULg et al

in Journal of Chemical Physics (1983), 79(8), 3719-3724

The Fourier transform of an electronic spectrum leads to an autocorrelation function which provides information on the propagation of the wave packet on the potential energy surface of the electronic ... [more ▼]

The Fourier transform of an electronic spectrum leads to an autocorrelation function which provides information on the propagation of the wave packet on the potential energy surface of the electronic state reached in the transition. The formula is valid even when nonadiabatic interaction is present, i.e., when the wave packet splits at a particular surface crossing with one part branching off to another potential energy surface. An explicit expression of the correlation function is given for a model of several discrete states interacting with a continuum. Closed-form solutions are given in the case of one and two resonances. A very simple formula valid in the strong coupling limit is also derived. The method is applied to the photoelectron spectrum of state A 2Sigma+ of HBr+, which is shown to correspond to the strong couplig case. [less ▲]

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