References of "Leyh, Bernard"
     in
Bookmark and Share    
Full Text
See detailLes valeurs et l'école. Atelier n°6
Gilles, Jean-Luc ULiege; Leyh, Bernard ULiege; Voos, Marie-Catherine ULiege

in Puzzle (2009), 25

Detailed reference viewed: 86 (10 ULiège)
Full Text
Peer Reviewed
See detailMedium and High Resolution Vacuum UV Photoabsorption Spectroscopy of Methyl Iodide (CH3I) and its deuterated isotopomers CD3I and CH2DI. A Rydberg series Analysis.
Locht, Robert ULiege; Leyh, Bernard ULiege; Jochims, H.-W. et al

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

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

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

Detailed reference viewed: 81 (12 ULiège)
Full Text
Peer Reviewed
See detailDetection of Oligonucleotide Gas-Phase Conformers: H/D Exchange and Ion Mobility as Complementary Techniques
Balbeur, Dorothée ULiege; Widart, Joëlle ULiege; Leyh, Bernard ULiege et al

in Journal of the American Society for Mass Spectrometry (2008), 19(7), 938-946

Gas-phase hydrogen/deuterium exchange of small oligonucleotides (dTG, dC6 and C6) with CD3OD was performed in the second hexapole of a Fourier transform ion-cyclotron resonance (FTICR) mass spectrometer ... [more ▼]

Gas-phase hydrogen/deuterium exchange of small oligonucleotides (dTG, dC6 and C6) with CD3OD was performed in the second hexapole of a Fourier transform ion-cyclotron resonance (FTICR) mass spectrometer. Ion activation experiments were conducted by accelerating the ions at the entrance of the H/D exchange cell under conditions promoting exclusively collisional isomerization. These experiments allowed us to assess the presence of several conformers, and to probe the height of the isomerization barrier separating these conformers. Ion mobility experiments were also performed. Their results were consistent with the H/D exchange data. A model accounting for the competing isomerization and H/D exchange reactions is proposed. Comparing the ion acceleration experiments for H/D exchange and for ion mobility reveals that the most compact conformer displays the fastest H/D exchange. This observation shows that H/D exchange and ion mobility provide us with complementary information because hydrogen accessibility and macromolecule compactness are not univocally associated. [less ▲]

Detailed reference viewed: 48 (13 ULiège)
Full Text
Peer Reviewed
See detailCore-Shell-Corona Micelles by PS-b-P2VP-b-PEO Copolymers: Focus on the Water-Induced Micellization Process
Willet, Nicolas ULiege; Gohy, Jean-François; Auvray, Loïc et al

in Langmuir (2008), 24(7), 3009-3015

It is now well established that amphiphilic PS-b-P2VP-b-PEO linear triblock copolymers can form multilayered assemblies, thus core-shell-corona (CSC) micelles, in water. Micellization is triggered by ... [more ▼]

It is now well established that amphiphilic PS-b-P2VP-b-PEO linear triblock copolymers can form multilayered assemblies, thus core-shell-corona (CSC) micelles, in water. Micellization is triggered by addition of a small amount of water into a dilute solution of the PS-b-P2VP-b-PEO copolymer in a non-selective organic solvent. However, the phenomena that take place at the very beginning of this process are poorly documented. How these copolymer chains are perturbed by addition of water was investigated in this work by light and neutron scattering techniques and transmission electron microscopy. It was accordingly possible to determine the critical water concentration (CWC), the compactness of the nano-objects in solution, their number of aggregation, and their hydrodynamic diameter at each step of the micellization process. [less ▲]

Detailed reference viewed: 104 (22 ULiège)
Full Text
Peer Reviewed
See detailMass Spectrometric Study of the Ionized C60: (Gamma-Cyclodextrin)2 Inclusion Complex by Collision Induced Dissociation
Greisch, Jean-François ULiege; Kyritsoglou, S.; Leyh, Bernard ULiege et al

in Journal of Mass Spectrometry [=JMS] (2008), 43(2), 242-50

The water soluble inclusion complex [C(60):(gamma-cyclodextrin)(2)] has been characterized using electrospray tandem mass spectrometry and collision induced dissociation. [C(60):(gamma-cyclodextrin)(2 ... [more ▼]

The water soluble inclusion complex [C(60):(gamma-cyclodextrin)(2)] has been characterized using electrospray tandem mass spectrometry and collision induced dissociation. [C(60):(gamma-cyclodextrin)(2)] ions were detected in the gas phase as doubly deprotonated, doubly protonated and doubly sodiated ions. The absence of monocharged complex ions following electronebulization is a likely consequence of the dimeric nature and structural symmetry of the inclusion complex. The collision induced dissociation of positive ions led exclusively to the observation of the protonated and sodiated cyclodextrin ions as well as their fragments. In negative ion mode the closed shell anion C(60)H(-) was the dominant fragment detected at low collision energies whereas at higher collision energies the signal corresponding to deprotonated cyclodextrin units becomes significant. Since C(60) (2-) has been reported to have a nonnegligible basicity compared to C(60) and C(60) (-), it is likely that the proton transfer involved in the formation of the C(60)H(-) anion occurs following transfer of the two electrons from the deprotonated gamma-cyclodextrins to the fullerene. Finally, the charge state of the inclusion complex ions is also shown to affect the interaction strengths between its subunits. The relative stabilities of the three ionic species studied in gas phase following electronebulization are as follows: [C(60):(gamma-cyclodextrin)(2) + 2H](2+) < [C(60):(gamma-cyclodextrin)(2)- 2H](2-) < [C(60):(gamma-cyclodextrin)(2) + 2Na](2+). [less ▲]

Detailed reference viewed: 64 (6 ULiège)
Full Text
Peer Reviewed
See detailThe Role of Long-Range Forces in the Determination of Translational Kinetic Energy Release. Loss of C4H4+ from Benzene and Pyridine Cations.
Gridelet, E.; Locht, Robert ULiege; Lorquet, Andrée ULiege et al

in Journal of Physical Chemistry A (2008), 112

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

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

Detailed reference viewed: 69 (16 ULiège)
Full Text
Peer Reviewed
See detailFast multiresponsive micellar gels from a smart ABC triblock copolymer
Willet, Nicolas ULiege; Gohy, Jean-François; Lei, Liangcai et al

in Angewandte Chemie (International ed. in English) (2007), 46(42), 7988-7992

The triblock copolymer PS-b-P2VP-b-PEO undergoes simultaneous micellization and gelation, leading to high-storage-modulus materials that have fast responses to pH value, temperature, ionic strength, and ... [more ▼]

The triblock copolymer PS-b-P2VP-b-PEO undergoes simultaneous micellization and gelation, leading to high-storage-modulus materials that have fast responses to pH value, temperature, ionic strength, and shearing. The gel has a hierarchical structure with spherical core-shell-corona micelles, which, in turn, pack closely into an ordered cubic structure. [less ▲]

Detailed reference viewed: 63 (20 ULiège)
Full Text
See detailpH-responsive micelles in dilute and gel-like media
Willet, Nicolas ULiege; Leyh, Bernard ULiege; Gohy, Jean-François et al

Conference (2006, June)

Detailed reference viewed: 6 (0 ULiège)
Full Text
See detailThe VUV Photoabsorption Spectroscopy and Photoionization of Halogenated Etylenes: Bromo-derivatives.
Locht, Robert ULiege; Leyh, Bernard ULiege; Jochims, H.-W. et al

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

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

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

Detailed reference viewed: 36 (7 ULiège)
Full Text
See detailThe Photoabsorption and Photoionization of Bromine revisited.
Locht, Robert ULiege; Leyh, Bernard ULiege; Jochims, H.-W. et al

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

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

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

Detailed reference viewed: 64 (16 ULiège)
Full Text
Peer Reviewed
See detailHydrogen atom loss from the benzene cation. Why is the kinetic energy release so large?
Gridelet, E.; Lorquet, Andrée ULiege; Locht, Robert ULiege et al

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

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

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

Detailed reference viewed: 74 (6 ULiège)
Full Text
Peer Reviewed
See detailAnalysis of kinetic energy release distributions by the maximum entropy method.
Leyh, Bernard ULiege; Gridelet, E.; Locht, Robert ULiege et al

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

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

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

Detailed reference viewed: 76 (11 ULiège)
Full Text
Peer Reviewed
See detailAbout the Photoionization of Methyl Bromide (CH3Br). Photoelectron and Photoionization Mass Spectrometric Investigation.
Locht, Robert ULiege; Leyh, Bernard ULiege; Dehareng, Dominique ULiege et al

in Chemical Physics (2006), 323

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

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

Detailed reference viewed: 117 (27 ULiège)
Full Text
Peer Reviewed
See detailThe vacuum UV photoabsorption spectrum of methyl bromide (CH3Br) and its perdeuterated isotopomer CD3Br: a Rydberg series analysis
Locht, Robert ULiege; Leyh, Bernard ULiege; Jochims, H.-W. et al

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

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

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

Detailed reference viewed: 61 (10 ULiège)
Full Text
Peer Reviewed
See detailConcomitant adsorption of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers and sodium dodecyl sulfate at the silica-water interface
Vangeyte, Patrick; Leyh, Bernard ULiege; De Clercq, C. et al

in Langmuir (2005), 21(17), 7710-7716

Upon addition of silica to aqueous solutions of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers (PEO-b-PCL) and sodium dodecyl sulfate (SDS), adsorption of the solutes occurs at the silica ... [more ▼]

Upon addition of silica to aqueous solutions of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers (PEO-b-PCL) and sodium dodecyl sulfate (SDS), adsorption of the solutes occurs at the silica-water interface. The amount of the adsorbed constituents has been measured by the total concentration depletion method. Small-angle neutron scattering experiments (SANS) have been carried out to investigate the structure of the adsorbed layer. Although SDS is not spontaneously adsorbed onto hydrophilic silica, adsorption is observed in the presence of PEO-b-PCL diblocks, in relation to the relative concentration of the two compounds. Conversely, SDS has a depressive effect on the adsorption of the copolymer, whose structure at the interface is modified. Copolymer desorption is however never complete at high SDS content. These observations have been rationalized by the associative behavior of PEO-b-PCL and SDS in water. [less ▲]

Detailed reference viewed: 44 (5 ULiège)