References of "Leyh, Bernard"
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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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See detailPhotoelectron Spectroscopy of Vinyl Bromide and Intramolecular Dynamics of the ionic B state.
Hoxha, A.; Locht, Robert ULg; Leyh, Bernard ULg et al

in Chemical Physics (2000), 256

In this paper we report the He(I) photoelectron spectrum (PES) and the threshold photoelectron spectrum (TPES) of C2H3Br. The fine structure in the first two ionic states in the He(I) spectrum is assigned ... [more ▼]

In this paper we report the He(I) photoelectron spectrum (PES) and the threshold photoelectron spectrum (TPES) of C2H3Br. The fine structure in the first two ionic states in the He(I) spectrum is assigned to progressions belonging partially to previously unobserved vibrational modes. The TPES has been measured between 9.0 and 25.0 eV, and the photon energy range of 9.8-12.0 eV has been investigated in more detail. Extensive calculations with the GAUSSIAN set of programs have been performed to help in the assignment of the observed features. Furthermore, a conical intersection between the A2A" and the B2A" states was found to take place along the C-Br stretching coordinate. Intramolecular dynamics of the B2A" state, initially prepared in the Franck-Condon region, was probed by the Fourier transform of the spectrum. The B2A" state is almost readily depleted, most probably due to a very effective internal cnversion through the conical intersection. [less ▲]

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See detailUn site internet dédié à la réactivation des bases de chimie à l'entrée à l'Université
Müller, Robert; Cornélis, André; Cahay, René et al

in Chimie Nouvelle (1999), 17

http:/ /www.ulg.ac.be/grptrans/ : sur ce site, nous mettons à Ia disposition de Ia communauté éducative (étudiants et enseignants) un outil intégré d'évaluation interactive et de réactivation des notions ... [more ▼]

http:/ /www.ulg.ac.be/grptrans/ : sur ce site, nous mettons à Ia disposition de Ia communauté éducative (étudiants et enseignants) un outil intégré d'évaluation interactive et de réactivation des notions fondamentales de chimie à la charnière entre I'Enseignement Secondaire et I'Université. [less ▲]

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See detailUnimolecular reaction dynamics from kinetic energy release distributions. III. A comparative study of the halogenobenzene cations
Urbain, P.; Leyh, Bernard ULg; Remacle, Françoise ULg et al

in Journal of Chemical Physics (1999), 110(2-12), 2911-2921

The translational kinetic energy release distribution (KERD) in the halogen loss reaction of the chloro-, bromo-, and iodobenzene cations has been experimentally determined in the microsecond time scale ... [more ▼]

The translational kinetic energy release distribution (KERD) in the halogen loss reaction of the chloro-, bromo-, and iodobenzene cations has been experimentally determined in the microsecond time scale and theoretically analyzed by the maximum entropy method. The KERD is constrained by the square root of the translational energy, i.e., by the momentum gap law. This can be understood in terms of quantum-mechanical resonances controlled by a matrix element involving a localized bound state and a rapidly oscillating continuum wave function, as in the case of a vibrational predissociation process. The energy partitioning between the reaction coordinate and the set of the remaining coordinates is nearly statistical, but not quite: less translational energy is channeled into the reaction coordinate than the statistical estimate. The measured entropy deficiency leads to values of the order of 80% for the fraction of phase space sampled by the pair of fragments with respect to the statistical value. In the case of the dissociation of the chlorobenzene ion, it is necessary to take into account a second process which corresponds to the formation of the chlorine atom in the excited electronic state 2P 1/2 in addition to the ground state 2/ 1/2. The observations are compatible with the presence of a small barrier (of the order of 0.12 eV) along the reaction path connecting the D̃ 2A 1 state of C 6H 5Cl + to the Cl( 2P 1/2) + C 6H 5 +(X̃ 1A 1) asymptote. © 1999 American Institute of Physics. [less ▲]

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See detailUnimolecular reaction dynamics from kinetic energy release distributions.IV. Dissociation of the Pyridine ion.
Urbain, P.; Leyh, Bernard ULg; Remacle, Françoise ULg

in International Journal of Mass Spectrometry and Ion Processes (1999), 185-187

The kinetic energy release distribution (KERD) for the dissociation of the Pyridine ion into C4H4++HCN in the microsecond time window has been experimentally determined and theoretically analyzed by the ... [more ▼]

The kinetic energy release distribution (KERD) for the dissociation of the Pyridine ion into C4H4++HCN in the microsecond time window has been experimentally determined and theoretically analyzed by the maximum entropy method. Less energy is channeled into the reaction coordinate than the statistical estimate because of the action of the "moentum gap law". The larger the value of the relative translational momentum of the fragments, the less efficient the exploration of phase space. the fraction of phase space efficiently sampled is estimated to be of the order of 75%. [less ▲]

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See detailUnimolecular Dynamics from Kinetic Energy Release Distributions. V. How does the Efficiency of Phase Space Sampling vary with Internal Energy?
Hoxha, A.; Locht, Robert ULg; Lorquet, Andrée ULg et al

in Journal of Chemical Physics (1999), 111(20), 9259-9266

A retarding field technique coupled with a quadrupole mass analyzer has been used to obtain the kinetic energy release distributions (KERDs) for C2H3Br+->[C2H3]++Br dissociation as a function of the ... [more ▼]

A retarding field technique coupled with a quadrupole mass analyzer has been used to obtain the kinetic energy release distributions (KERDs) for C2H3Br+->[C2H3]++Br dissociation as a function of the internal energy. The KERDs obtained by dissociative photoionization using the He(I), Ne(I) and Ar(II) resonance lines were analyzed by the maximum entropy method and were found to be well described by introducing a single dynamical constraint, namely the relative translational momentum of the fragments. Ab initio calculations reveal the highly fluxional character of the C2H3+ ion. As the energy increases, several vibrational modes are converted in turn into large-amplitude motions. Our main result is that, upon increasing internal energy, the fraction of phase space sampled by the pair of dissociating fragments is shown to first decrease, pass through a shallow minimum around 75%, and then increase again, reaching almost 100% at high internal energies (8 eV). This behaviour at high internal energies is interpreted as resulting from the conjugated effect of intramolecular vibrational redistribution (IVR) and radiationless transitions among potential energy surfaces. Our findings are consistent with the coincidence data of Miller and Bear, reanalyzed here, and with the KERD of the metastable dissociation. [less ▲]

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See detailThe Vacuum UV Photoabsorption Spectrum of Methyl Fluoride (CH3F). A vibrational Analysis.
Locht, Robert ULg; Hoxha, A.; Leyh, Bernard ULg et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H (1999)

The vacuum photoabsorption spectrum of CH3F has been recorded using synchrotron radiation dispersed at medium resolution. Special data handling has been applied. The vibrational structure of about 70 ... [more ▼]

The vacuum photoabsorption spectrum of CH3F has been recorded using synchrotron radiation dispersed at medium resolution. Special data handling has been applied. The vibrational structure of about 70 features has been analyzed for the first time. [less ▲]

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See detailThe Spectroscopy of Ethylene and its Derivatives. C2H4 and the three C2H2FCl isomers. The CIS- and Threshold Photoelectron Spectra.
Locht, Robert ULg; Leyh, Bernard ULg; Hottmann, K. et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H (1999)

The Cis- and threshold photoelectron spectra of C2H4 and the three isomers of C2H2FCl are measured using synchrotron radiation. A short analysis has also been reported.

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See detailThe Photoionization of Vinyl Bromide Clusters.
Hoxha, A.; Locht, Robert ULg; Leyh, Bernard ULg et al

Book published by Berliner Elektronen Speicherring für Synchrotron Sthrahlung m.b.H (1999)

The optimization of the conditions for cluster production from C2H3Br is investigated. The dissociative photoionization of these species is reported, e.g. [C2H2Br]2+->C4H6Br++Br. An intracluster Penning ... [more ▼]

The optimization of the conditions for cluster production from C2H3Br is investigated. The dissociative photoionization of these species is reported, e.g. [C2H2Br]2+->C4H6Br++Br. An intracluster Penning ionization phenomenon is observed. [less ▲]

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See detailKinetic Energy Release Distributions in the Dissociation of Energy-Selected Fluoroethene and 1,1-Difluoroethene Ions.
Güthe, F.; Locht, Robert ULg; Leyh, Bernard ULg et al

in Journal of Physical Chemistry A (1999), 103

The unimolecular dissociation of energy-selected fluoroethene and 1,1-difluoroethene ions has been investigated by threshold photoelectron photoion coincidence TPEPICO) technique. The breakdown diagrams ... [more ▼]

The unimolecular dissociation of energy-selected fluoroethene and 1,1-difluoroethene ions has been investigated by threshold photoelectron photoion coincidence TPEPICO) technique. The breakdown diagrams of the 1,1-difluorethene and fluoroethene have been recorded between 13-22 eV. From time-of-flight (TOF) spectra, complete distributions of the kinetic energy released (KERD) in the dissociation of these energy-selected ions have been derived. For the HF-loss reaction channel, the KERD peaks at about 200 meV for low excitation energies but becomes thermal at higher excitation energies. For the F-loss channel, the KERD peaks at zero kinetic energy for low excitation energies but at about 200 meV for high excitation energy. The analysis of the KERD provides evidence that consecutive fragmentation takes place for the 1,1-difluoroethene at energies above 19 eV. [less ▲]

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See detailThree-dimensional Kinetic Energy Distributions of Ions using a Retarding Potential Analyser. Analysis of Discimination Effects by Ion Trajectory Simulations.
Hoxha, A.; Leyh, Bernard ULg; Locht, Robert ULg

in Rapid Communications in Mass Spectrometry : RCM (1999), 13

This paper presents a method of extracting three-dimensional kinetic energy distributions from retarding potential curves, suitable for analysing low kinetic energy releases. Trajectory calculations were ... [more ▼]

This paper presents a method of extracting three-dimensional kinetic energy distributions from retarding potential curves, suitable for analysing low kinetic energy releases. Trajectory calculations were performed which led to an analytical function correcting for the influence of discrimination against ions with velocity components perpendicular to the retarding field direction. The analysis of the thermal kinetic energy distribution of molecular vinyl bromide ions confirms the computed correcting factor. [less ▲]

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See detailShear-induced order in aqueous micellar solutions of amphiphilic poly(tert-butylstyrene)-b-poly(Na methacrylate) diblock
Leyh, Bernard ULg; Creutz, S.; Gaspard, J. P. et al

in Macromolecules (1998), 31(26), 9258-9264

Shear-induced order of aqueous micellar solutions of a poly(tert-butylstyrene)-b-poly(sodium methacrylate) diblock (c ) 2.5-15 w/v %) has been investigated by small-angle X-ray scattering. Data collected ... [more ▼]

Shear-induced order of aqueous micellar solutions of a poly(tert-butylstyrene)-b-poly(sodium methacrylate) diblock (c ) 2.5-15 w/v %) has been investigated by small-angle X-ray scattering. Data collected from a Couette cell in both radial and tangential geometries agree with a crystalline ordering of micelles in close packed hexagonal layers perpendicular to the velocity gradient, when c is in the 5-10 w/v % range. The measured interlayer distance is indeed very close to the value expected for a closepacked structure. The experimental data are consistent with a zigzag motion of adjacent planes upon shear. Shear-induced order is, however, restricted to a narrow concentration range just above the concentration for the sol-gel transition. This domain is thought to correspond to a regime where relative layer translation modes are allowed whereas mutual rotation is hindered. [less ▲]

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See detailReactivity of Halogenoethylene Ions using Photoionization and Collisional Activation.
Leyh, Bernard ULg; Hoxha, A.; Franck, B. et al

in Karjalainen, E. J.; Hesso, A. E.; Jalonen, J. E. (Eds.) et al Advances in Mass Spectrometry: Volume 14. (1998)

Unimolecular reactivity of ionized difluoroethylene and vinylbromide have been investigated using photoionization mass spectrometry and tandem mass spectrometry. Kinetic energy release distributions ... [more ▼]

Unimolecular reactivity of ionized difluoroethylene and vinylbromide have been investigated using photoionization mass spectrometry and tandem mass spectrometry. Kinetic energy release distributions corresponding to HF- and F- losses from 1,1-C2H2F2+ and to Br-loss from C2H3Br+ have been determined. At low internal energy the loss of HF from C2H2F2+ leads to the fluoroacetylene cation with a large kinetic energy release (0.4-2.5 eV) while at higher energy a new channel is opened, leading to C=CHF+ (fluorovinylidene) with a much smaller kinetic energy release (0.0-0.2 eV). For the F-loss from C2H2F2+ and the Br-loss from C2H3Br+ bimodal distributions have been observed. The possible role of excited states in these dissociations is discussed. [less ▲]

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See detailThe Photoionization of small Vinyl Bromide (C2H3Br)n Clusters.
Hoxha, A.; Leyh, Bernard ULg; Locht, Robert ULg et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H (1998)

The ionization and decomposition of small clusters produced from C2H3Br are investigated by threshold photoelectron-photoion coincidence spectroscopy.

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See detailThe threshold Photoelectron-Photoion Coincidence Spectroscopy of Vinyl Bromide (C2H3Br).
Hoxha, A.; Leyh, Bernard ULg; Locht, Robert ULg

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H (1998)

The dissociative ionization of C2H3Br has been investigated by threshold photoelectron-photoion coincidence spectroscopy using synchrotron radiation. The C2H3+, C2H2+, HBr+ and Br+ dissociation channels ... [more ▼]

The dissociative ionization of C2H3Br has been investigated by threshold photoelectron-photoion coincidence spectroscopy using synchrotron radiation. The C2H3+, C2H2+, HBr+ and Br+ dissociation channels were considered. [less ▲]

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See detailAbsorption and Ionization Spectroscopy of Methyl Halides and Deuterated Methyl halides between 6 and 12 eV.
Locht, Robert ULg; Leyh, Bernard ULg; Jochims, H.-W. et al

Book published by Berliner Elektronen Speicherring für Synchrotron Strahlung m.b.H (1998)

The vacuum UV photoabsorption spectrum of CH3Cl and CD3Cl have been measured between 6 and 12 eV photon energy. The photoionization efficiency curve of CH3+ provided by dissociative photoionization of ... [more ▼]

The vacuum UV photoabsorption spectrum of CH3Cl and CD3Cl have been measured between 6 and 12 eV photon energy. The photoionization efficiency curve of CH3+ provided by dissociative photoionization of CH3Cl is reported. The attention is focussed on the ion-pair CH3+/Cl- formation. [less ▲]

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See detailA He(I) Photoelectron Spectroscopic Study of the X2A"2state of NH3+ and ND3+. A Reanalysis and evidence for the Coriolis Coupling between the Bending nu2 and nu4 Modes.
Locht, Robert ULg; Leyh, Bernard ULg; Hottmann, K. et al

in Chemical Physics (1998), 233

In the He(I) photoelectron spectrum of NH3 and its isotopomer ND3 the complete vibrational structure of the X2A"2 state of NH3+ and ND3+ is examined in detail. Three vibrational progressions are ... [more ▼]

In the He(I) photoelectron spectrum of NH3 and its isotopomer ND3 the complete vibrational structure of the X2A"2 state of NH3+ and ND3+ is examined in detail. Three vibrational progressions are identified. The well-known strongest progression, already unambiguously assigned to the nu2 out-of-plane bending mode, is observed from v=0-17 in NH3+ and v=0-20 in ND3+. For NH3+ this vibration could be characterized not only by its energy hcomega2= 0.109+/-0.001 eV (or omega2= 878+/-7 cm-1) but also by its first anharmonicity constant hcomega22x22=-(16.2+/-1.2)10-4 eV (or omega22x22=-13.0+/-1.0 cm-1). The best fit of the experimental data required the introduction of a second anharmonicity constant, i.e. hcomega22y22= -(30.7+/-4.2)x10-6 eV (or omega22y22=-0.248+/-0.034 cm-1). The earlier reported weak progression assigned to the vibrational combination nu1+nnu2 transitions has been reexamined. Suitable handling of the data leads to two possible energies for the nu1 degenerate NH stretching vibrational normal mode, i.e. hcomega1 =0.306+/-0.006 eV or 0.422+/-0.005 eV. Several arguments are brought to favour the value of hcomega1=0.422 eV (or omega1=3404 cm-1). Finally a third weak progression, reported for the first time, is assigned to nu4+nnu2 transitions where the nu4 in-plane bending mode is optically forbidden. This vibrational normal mode is characterized by an energy hcomega4=0.186+/-0.010 eV (omega4=1500+/-80 cm-1). In agreement with the theoretical predictions, this transition becomes allowed through a strong Coriolis vibro-rotational coupling between the nu4 and the nu2 vibrational normal modes. The same measurements and the isotope effect on the molecular constants are investigated in ND3+ too. [less ▲]

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See detailL'enseignement de la chimie aux étudiants du secondaire qui se destinent à l'université: Trois heures de chimie valent mieux qu'une
Cornélis, André ULg; Cahay, René ULg; Leyh, Bernard ULg

in Chimie Nouvelle (1998), 16

The major importance of a high quality chemistry education in secondary schools is highlighted by the analysis of the results of a procedure developed at the University of Liège to help the students ... [more ▼]

The major importance of a high quality chemistry education in secondary schools is highlighted by the analysis of the results of a procedure developed at the University of Liège to help the students starting their university education, to evaluate their level of basic chemistry competences and to improve them if necessary. It turns out that students who followed three weekly periods of chemistry per week in the secondary school are clearly favoured compared to those who had only one period. These discrepancies show up not only on the starting competence level but also on the progress realized during the remediation step. The starting competence level influences also the strategy chosen by the student for his/her individual remediation. [less ▲]

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See detailPhotoabsorption, He(I) and Threshold Photoelectron spectra and CIS-Spectroscopy of Vinylchloride.
Locht, Robert ULg; Leyh, Bernard ULg; Hottmann, K. et al

in Aumayr, F.; Betz, G.; Winter, H. P. (Eds.) XX. ICPEAC: Scientific Programme and Abstracts of Contributed Papers. Volume 1. (1997)

The Vacuum UV photoabsorption and Threshold Photoelectron spectra of C2H3Cl have been measured by using synchrotron radiation. Vibrationally resolved CIS-spectroscopy of the same molecule is also reported.

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