Document Server@UHasselt
(3.247 recursos)
Repository of the University of Hasselt containing publications in the fields of statistics, computer science, information strategies and material from the Institute for behavioural sciences.
Mostrando recursos 1 - 14 de 14
1.
Structural, Rotational, Vibrational, and Electronic Properties of Ionized Carbon Clusters Cn+ (n = 4-19) - Giuffreda, M.G.; Deleuze, M.S.; François, J.P.
The structures, rotational moments, vibrational normal modes, and infrared spectra of small to medium-size ionized carbon clusters Cn+ (n = 4-19) are investigated using density functional (DFT) and coupled cluster (CC) theories. Comparison is made with the neutral systems from which they derive. In contrast to previous restricted open-shell Hartree-Fock (ROHF) results by von Helden and co-workers, electron correlation is shown to strongly limit distortions of the structure upon an adiabatic ionization process. Nonetheless, for such a process, the C4n+2 and to a lesser extent the C4n+1 cyclic systems are found to evolve from an essentially regular (i.e., cumulenic) pattern...
2.
Structural, Rotational, Vibrational, and Electronic Properties of Carbon Cluster Anions Cn- (n = 3-13) - Giuffreda, M.G.; Deleuze, M.S.; François, J.P.
The structural, rotational, and vibrational properties of Cn- clusters (n = 3-13) have been investigated by means of density functional theory (DFT/B3LYP) and, whenever possible, coupled cluster (CC) theory along with the aug-cc-pVDZ basis set. These properties are compared with those of their neutral counterparts and of the corresponding cations. The linear and merely cumulenic chains undergo a substantial increase of the bond-length alternation and an increase of size upon adiabatic electron attachment. In addition, most chains (C5, C7, C8, C9, and C10) become slightly bent in their anionic form because of Renner-Teller effects. The structural outcomes of such processes...
3.
Probing Molecular Conformations with Electron Momentum Spectroscopy: The Case of n-Butane - Deleuze, M.S.; Pang, W.N.; Shang, R.C.; Salam, A.
High-resolution (e,2e) measurements of the valence electronic structure and momentum-space electron density distributions of n-butane have been exhaustively reanalyzed in order to cope with the presence of two stable structures in the gas phase, namely the all-staggered and gauche conformers. The measurements are compared to a series of Boltzmann-weighted simulations based on the momentum-space form of Kohn-Sham (B3LYP) orbital densities, and to ionization spectra obtained from high-level [ADC(3)] one-particle Green's Function calculations. Indubitable improvements in the quality of the simulated (e,2e) ionization spectra and electron momentum profiles are seen when the contributions of the gauche form of n-butane are included....
4.
Can Benzylic Amide [2]Catenane Rings Rotate on Graphite? - Deleuze, M.S.
The structure and dynamics of two benzylic amide [2]catenanes, bearing phenyl- or thiophenyl-1,3-dicarbonyl groups and physisorbed onto a graphite surface, have been investigated by means of molecular mechanics along with elementary calculations of kinetic rate constants. For the isophthaloyl-based catenane (1), a delicate balance between enthalpy and entropy effects is pointed out. On one hand, van der Waals interactions are enhanced in a first series of co-conformations (A), including the global energy minimum, which are characterized by a near-parallel deposition and flattening of both macrocycles onto the graphite layer. On the other hand, vibrational entropy is shown to favor a...
5.
Outer-Valence Green's Function Study of Cycloalkane and Cycloalkyl-Alkane Compounds - Deleuze, M.S.; Delhalle, J.
In this contribution, we report a quantitative analysis of gas-phase ultraviolet photoelectron spectra (HeI) of model compounds such as cyclopentane, cyclohexane, and cycloalkyl-1-alkane derivatives, by means of outer-valence Green's function (OVGF) calculations. These spectra and their OVGF theoretical simulations are also compared with UPS measurements on -cycloalkyl--alkanethiol monolayers adsorbed on gold. This theoretical study analyses the dependence of valence ionization spectra of saturated hydrocarbons on structural characteristics (configuration, conformation, and torsional flexibility).
6.
From Sulfoxide Precursors to Model Oligomers of Conducting Polymers - Claes, L.; François, J.P.; Deleuze, M.S.
The gas-phase internal elimination (Ei) reaction of the sulfoxide (-SO-CH3) precursors of ethylene and model oligomers of PPV and PITN has been investigated by means of Hartree-Fock, Mller-Plesset (second and fourth order), and Density Functional Theory (B3LYP, MPW1K) calculations. Considerable differences between the obtained ground state and transition state geometries and the calculated activation energies are observed from one approach to the other, justifying first a careful calibration against the results of a benchmark CCSD(T) study of the Ei reaction leading to ethylene. In comparison with the CCSD(T) results, as well as with available experimental data, DFT calculations along with...
7.
Ionization Bands and Electron Affinities of Mixed Boron-Nitrogen BnNn Clusters (n = 3,4,5) - Deleuze, M.S.; Giuffreda, M.G.; François, J.P.; Cederbaum, L. S.
The ionization bands and electron affinities of medium-size BnNn clusters (n = 3, 4, 5) have been investigated by means of one-particle Green's function calculations using the outer-valence Green's function (OVGF) approximation or the third-order algebraic diagrammatic construction [ADC(3)] scheme. Despite their structural similarity with isoelectronic cumulenic carbon chains and rings, these clusters do not exhibit a significant breakdown of the orbital picture of ionization, with the exception of the N2s bands (b > 25 eV), which relate exclusively to complex sets of shake-up lines. The main (one-hole) ionization bands provide specific signatures for ring topologies based on n equivalent...
8.
Structural, Rotational, and Vibrational Properties of Mixed Ionized Boron-Nitrogen Clusters BnNn+ (n = 3-10) - Giuffreda, M.G.; Deleuze, M.S.; François, J.P.
The structural, rotational, and vibrational properties of BnNn+ clusters (n = 3-10) have been investigated using density functional theory (DFT) and compared with that of their neutral counterparts. The BnNn+ species with n = 4, 6, 8, 10 are found to possess as lowest energy form a fully regular structure of Dnh symmetry, as the neutral species. In both cases, their IR vibrational spectrum invariably contains four lines, relating to one out-of-plane nondegenerate and three in-plane doubly degenerate normal modes. On the other hand, the BnNn clusters with n = 3, 5, 7, 9 are found to evolve from a...
9.
Theoretical Study of the Conversion of Sulfonyl Precursors into Chains of Poly(p-phenylene vinylene) - Claes, L.; François, J.P.; Deleuze, M.S.
The elimination and side reactions involved in the thermal conversion of sulfonyl precursor chains into poly(p-phenylene vinylene) (PPV) have been studied in detail, using Density Functional theory, along with the MPW1K functional. The performance of the MPW1K functional for describing radical dissociation and internal conversion reactions of sulfonyl precursors has been assessed against the results of benchmark CCSD(T) calculations. Enthalpies as well as entropies are calculated at different temperatures at the level of the rigid rotor-harmonic oscillator approximation. Entropy effects on internal elimination reactions are very limited. In sharp contrast, at the temperatures under which the conversion is usually performed...
10.
Valence One-Electron and Shake-Up Ionization Bands of Carbon Clusters. III. The Cn (n = 5,7,9,11) Rings - Deleuze, M.S.; Giuffreda, M.G.; François, J.P.
The 1h (one-hole) and 2h-1p (two-hole; one-particle) shake-up bands in the valence ionization spectrum of odd-membered carbon rings (C5, C7, C9, C11) are investigated by means of the third-order algebraic diagrammatic construction [ADC(3)] scheme for the one-particle Green's function. Despite a severe dispersion of the - and - ionization intensity over intricately dense sets of satellites, the present study undoubtedly confirms that structural fingerprints in ionization spectra could be usefully exploited to discriminate the cyclic C5, C7, C9, and C11 species from their linear counterparts in plasma conditions. Such spectra could also be used to indirectly trace very fine details...
11.
Valence One-Electron and Shake-Up Ionization Bands of Polycyclic Aromatic Hydrocarbons. III. Coronene, 1.2,6.7-Dibenzopyrene, 1.12-Benzoperylene, Anthanthrene - Deleuze, M.S.
A comprehensive theoretical study of the He(I) UV photoionization spectra of coronene, 1.2,6.7-dibenzopyrene, 1.12-benzoperylene, and anthanthrene up to electron binding energies of ~18 eV is presented with the aid of one-particle Green's function calculations performed using the outer-valence Green's function (OVGF) approach and the third-order algebraic-diagrammatic construction [ADC(3)] scheme, using Dunning's correlation-consistent polarized valence basis set of double- quality and the 6-31G basis set, respectively. The deviations from the one-electron OVGF/cc-pVDZ binding energies and experimental results most generally do not exceed 0.3 eV. OVGF/cc-pVDZ pole strengths smaller than 0.85 systematically corroborate a breakdown of the orbital (or one-electron) picture of...
12.
Effect of Thermal Motions on the Structure and UV-Visible Electronic Spectra of Stilbene and Model Oligomers of Poly(p-Phenylene Vinylene) - Kwasniewski, S.P.; François, J.P.; Deleuze, M.S.
In the present study, we investigate the influence of temperature on the width and location of bands in the UV-visible absorption spectra of oligomer chains of poly(p-phenylene vinylene) (PPV). These spectra have been computed by means of molecular dynamics (MD) simulations along with the classical MM3 force field, in conjunction with (Z)INDO/S-CIS calculations of vertical excitation energies and transition moments. In addition, the MD(MM3) computations enable consistent insights into the average structures of cis- and trans-stilbene, at temperatures ranging from 0 to 500 K. For trans-stilbene and larger PV-n oligomer chains converging to PPV, thermal motions at room temperature in...
13.
Study of the photoelectron and electron momentum spectra of cyclopentene using benchmark Dyson orbital theories - HUANG, Yanru; Ning, Chuan G.; Deng, Jing K.; DELEUZE, Michael
A complete study of the valence electronic structure and related electronic excitation properties of cyclopentene in its C-s ground state geometry is presented. Ionization spectra obtained from this compound by means of photoelectron spectroscopy (He I and He II) and electron momentum spectroscopy have been analyzed in details up to electron binding energies of 30 eV using one-particle Green's function (1p-GF) theory along with the outer-valence (OVGF) and the third-order algebraic diagrammatic construction [ADC(3)] schemes. The employed geometries derive from DFT/B3LYP calculations in conjunction with the aug-cc-pVTZ basis set, and closely approach the structures inferred from experiments employing microwave spectroscopy...
14.
Cycloaddition reactions of ICNO - Pasinszki, Tibor; Krebsz, Melinda; HAJGATO, Balazs
The mechanism and selectivity of cycloaddition reactions of iodonitrile oxide, ICNO, have been studied with theoretical methods for the first time using MR-AQCC coupled-cluster and B3LYP DFT methods. Calculations have predicted that the favoured ICNO dimerisation process is a multi-step reaction to diiodofuroxan involving dinitrosoethylene-like intermediates. The ICNO cycloaddition with nitriles and ethynyl derivatives is a synchronous process favouring the formation of 1,2,4-oxadiazole and 1,2-oxazole derivatives, respectively. The cycloaddition reactions of ICNO have been studied experimentally by generating ICNO from AgCNO and iodine. Diiodofuroxan is obtained, however, even at the presence of nitriles. (c) 2009 Elsevier B.V. All rights reserved.
1.
