References of "Dehareng, Dominique"
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See detailCatalytic reaction pathways approached by quantum chemistry: a challenge
Dive, Georges ULg; Dehareng, Dominique ULg; Ghosez, Léon

in Cellular and Molecular Life Sciences : CMLS (1998), 54(4), 378-382

This review explores the potential of quantum chemistry to help understand complex biochemical reactions such as enzyme catalysis. Starting from a historical background, the article introduces the reader ... [more ▼]

This review explores the potential of quantum chemistry to help understand complex biochemical reactions such as enzyme catalysis. Starting from a historical background, the article introduces the reader to the great diversity of problems than can be dealt with in the framework of quantum chemistry. [less ▲]

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See detailRésistance bactérienne aux beta-lactamines
Charlier, Paulette ULg; Coyette, Jacques ULg; Dehareng, Dominique ULg et al

in Medecine Sciences : M/S (1998), 14(5), 544-555

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See detailProposition for the acylation mechanism of serine proteases: A one-step process?
Dive, Georges ULg; Dehareng, Dominique ULg; Peeters, Daniel

in International Journal of Quantum Chemistry (1996), 58(1), 85-107

This work proposes a very detailed ab initio study of the hypothesis for a one-step serine protease acylation process with one water molecule acting as the main catalyst reactant. For the 11 increasing ... [more ▼]

This work proposes a very detailed ab initio study of the hypothesis for a one-step serine protease acylation process with one water molecule acting as the main catalyst reactant. For the 11 increasing complexity models considered, the minimum and transition state conformations for the reaction are determined by full geometry optimizations at the ab initio self-consistent field (scF) levels within several basis sets, from MINI-1 to 6-31G, and, for the smallest complexes, at the post-SCF MP2 level within the 6-31G** basis set. The related thermodynamical quantities are calculated for all the conformations. The influence of the oxyanion hole stabilizer and of the dyad His57-Asp102 is quantified and a very good agreement is obtained with point mutagenesis. The activation barrier is found in the range 15-18 kcal/mol. (C) 1996 John Wiley & Sons, Inc. [less ▲]

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See detailEnergetic and conformational study of four benzylimidazole compounds with alpha 2 agonist profile: The mivazerol and three methylated derivatives
Vancampenhout, Nathalie; Dive, Georges ULg; Dehareng, Dominique ULg

in International Journal of Quantum Chemistry (1996), 60(4), 911-930

The mivazerol and three of its methylated derivatives are studied at the ab initio SCF level within the MINI-1 and 6-31G basis sets. This study aimed at determining some probable conformations, either ... [more ▼]

The mivazerol and three of its methylated derivatives are studied at the ab initio SCF level within the MINI-1 and 6-31G basis sets. This study aimed at determining some probable conformations, either neutral or protonated, that could interact with the alpha 2 adrenoceptors. The solvent effect was also studied within the Onsager's solvent model at the two dielectric constant (epsilon) values of 4 and 80. The interaction with the environment (either solvent or receptor) is schematically studied by positioning either two water molecules or one formamide or/and one formic add near the amide and the imidazole for few isomers. The medium polarization, through epsilon, and the solvation effect, through the interaction with the solvent molecules or the receptor side chains, stabilize the same isomers. Post-SCF calculations are performed at the CISD level, the first excited singlet and triplet states energies are determined, and the question of the wave-function stability is addressed. The results indicate the probability of a spin-orbit coupling with the first excited triplet state, thus opening the question of such a possibility within an enzyme active site. (C) 1996 John Wiley & Sons, Inc. [less ▲]

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See detailINTERVALENCE TRANSITIONS IN MIXED-VALENCE BIS(TETRATHIAFULVALENE) COMPOUNDS
Lahlil, Khalid; Moradpour, Alec; Bowlas, Christopher et al

in Journal of the American Chemical Society (1995), 117(40), 9995-10002

The series of new bis(tetrathiafulvalene) [bis(TTF)] compounds 10-12a,b have been synthetized with the TTF-like synthon 8a,b, previously used to prepare the pyrazine-fused bis(TTF) 7a,b. These compounds ... [more ▼]

The series of new bis(tetrathiafulvalene) [bis(TTF)] compounds 10-12a,b have been synthetized with the TTF-like synthon 8a,b, previously used to prepare the pyrazine-fused bis(TTF) 7a,b. These compounds exhibit four reversible sequential one-electron oxidation steps, on the basis of cyclic voltammetry. For the cation radicals 7b(.+), 10(.+), and 12(.+), generated electrochemically, rather intense and broad bands in the near-IR region, specific of class II mixed valence compounds, were found. Theoretical calculations at the semiempirical AM1 level as well as at the ab-initio level indicated that these cation radicals are charge-distributions localized as related to mixed valence species. These calculations also allowed the low-energy absorption bands to be assigned to intervalence transitions; these transitions imply the existence of multiple low-lying excited states that are non-adiabatically coupled to the ground-state of these open-shell species. [less ▲]

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See detailDetailed Study of a Molecule in a Molecule N-Acetyl-L-Tryptophanamide in a Active-Site Model of Alpha-Chymotrypsin
Dive, Georges ULg; Dehareng, Dominique ULg; Ghuysen, Jean-Marie ULg

in Journal of the American Chemical Society (1994), 116(6), 2548-2556

Six complexes between a model active site of alpha-chymotrypsin (261 atoms) and N-acetyl-L-tryptophanamide (33 atoms) were optimized at the semiempirical AM1 level. In one of these complexes, a water ... [more ▼]

Six complexes between a model active site of alpha-chymotrypsin (261 atoms) and N-acetyl-L-tryptophanamide (33 atoms) were optimized at the semiempirical AM1 level. In one of these complexes, a water molecule was included. A detailed study at the geometric and energetic levels is presented. The discussion deals with the nature of the interaction, the effect of the environment, the ligand deformation, the backbone relaxation, the water molecule freedom, and the comparison with the molecular mechanics results. [less ▲]

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See detailAnalytical calculation of the electrostatic interaction energy within the CNDO framework
Dehareng, Dominique ULg; Dive, Georges ULg; Ghuysen, Jean-Marie ULg

in International Journal of Quantum Chemistry (1993), 46(6), 711-734

This work analyses the adequacy of an analytical electrostatic energy formulation within the CNDO framework to predict the stable conformations of large molecular complexes. Comparisons are made with ab ... [more ▼]

This work analyses the adequacy of an analytical electrostatic energy formulation within the CNDO framework to predict the stable conformations of large molecular complexes. Comparisons are made with ab initio results for small systems such as water-formamide, methanol-water-imidazole, or guanine-cytosine and with AM1 results for two large systems: a molecular tweezer + the 9-methyladenine complex and a model active site of the alpha-chymotrypsin and its ligand complex. This approach is efficient in providing reliable conformers for large molecular systems in a very fast way. [less ▲]

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See detailPolarization correction of the electrostatic potential for aromatic-compounds - Study of the nucleophilic-attack
Dive, Georges ULg; Dehareng, Dominique ULg

in International Journal of Quantum Chemistry (1993), 46(1), 127-136

The electrostatic potential (EP) and the polarization correction (PL) on the EP were calculated for four aromatic compounds: benzene, chlorobenzene, phenol, and benzoic amide, at the ab initio SCF level ... [more ▼]

The electrostatic potential (EP) and the polarization correction (PL) on the EP were calculated for four aromatic compounds: benzene, chlorobenzene, phenol, and benzoic amide, at the ab initio SCF level within two basis sets: 6-31G** and MINI-1. One calculation was performed using the polarized MINI-1** basis set. The quantity total interaction energy (TEH) defined as -EP + PL can be used as an indicator of the nucleophilic attack preferential position. By reference to 6-31G**, MINI-I provides very satisfactory results. Moreover, the MINI-1** results are very similar to the MINI-I ones. It appears that -EP does not provide a reliable tool to study the nucleophilic attack susceptibility, whereas TEH seems to be very well adapted for this kind of approach. [less ▲]

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See detailEnergy Analysis on Small to Medium Sized H-Bonded Complexes
Dive, Georges ULg; Dehareng, Dominique ULg; Ghuysen, Jean-Marie ULg

in Theoretica Chimica Acta (1993), 85(6), 409-421

Dimers (water-methanol, guanine-cytosine) as well as trimers (methanol-water-imidazole, formamide-methylformate-formamide), are studied as H-bonded complexes of increasing complexity. All the investigated ... [more ▼]

Dimers (water-methanol, guanine-cytosine) as well as trimers (methanol-water-imidazole, formamide-methylformate-formamide), are studied as H-bonded complexes of increasing complexity. All the investigated conformations have been fully optimized. In particular, it is the first time that all the intra- and intermolecular parameters of the guanine-cytosine complex are left variable. In minimal basis sets, the planar conformation has been found to be a first-order critical point. The minimal basis set MINI-1 has been adapted to provide nearly planar amides. The stability of the complexes is accounted for by four energy components of the same order: the first-order term (electrostatic + exchange), the polarization, the charge transfer and the correlation terms. In the case of the studied trimers, the energy components, apart from the electrostatic one, have been found to be nearly additive. [less ▲]

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See detailA VARIABLE MECHANISM FOR THE NUCLEOPHILIC VINYLIC SUBSTITUTIONS IN A SERIES OF GEM-DIHALOGENATED ALKENES BY A BIDENTATE SULFUR NUCLEOPHILE - AN EXPERIMENTAL AND AM1 THEORETICAL-STUDY
Gimbert, Yves; Moradpour, Alec; Dive, Georges ULg et al

in Journal of Organic Chemistry (1993), 58(17), 4685-4690

The nucleophilic substitutions of a series of gem-dihalogenated alkenes 3,5,7,8, and 9 (RS)2C=CX2 (X = Cl, F) with 1,2-benzenedithiolate b have been studied. Depending on the structures of the R groups ... [more ▼]

The nucleophilic substitutions of a series of gem-dihalogenated alkenes 3,5,7,8, and 9 (RS)2C=CX2 (X = Cl, F) with 1,2-benzenedithiolate b have been studied. Depending on the structures of the R groups (alkyl, saturated and unsaturated cycloalkyls, aromatic ring), the course of the reactions and the structures of the yielded products are modified. In the frame of the addition-elimination-type mechanism for these nucleophilic substitutions, the energy contents of the anionic intermediates, resulting from the additions of the nucleophile b to the unsaturated centers, is calculated at the AM1 method level. For the compounds 5, 7, 8, and 9, the calculated energies nicely corroborate the experimental results. For 3, anionic intermediates are no longer found by calculation, and a synchronous single-step substitution is strongly suggested. [less ▲]

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See detailPolarization-corrected electrostatic potentials of aromatic compounds
Dehareng, Dominique ULg; Dive, Georges ULg; Ghuysen, Jean-Marie ULg

in Journal of the American Chemical Society (1993), 115(15), 6877-6882

The electrostatic potentials (EPS) corrected for polarization (TPS) of the aromatic compounds benzene, aniline, chlorobenzene, nitrobenzene, phenol, benzamide, and N-phenylacetamide have been calculated ... [more ▼]

The electrostatic potentials (EPS) corrected for polarization (TPS) of the aromatic compounds benzene, aniline, chlorobenzene, nitrobenzene, phenol, benzamide, and N-phenylacetamide have been calculated at the ab initio SCF level within three basis sets: 6-31G**, MINI-1, and STO-3G. For chlorobenzene in its MINI-1-optimized geometry, the calculation was also performed within MINI-1**. By reference to 6-31G**, the MINI-1-computed EP is much more satisfactory than the STO-3G-computed EP, whereas the MINI-I and STO-3G basis sets give very similar total potentials corrected for polarization (TPs). The MINI-1** basis set appears to be miscalibrated for computing EPs. It provides qualitative results that differ from those obtained with the 6-31G** basis set. The EP has a negative well above the middle of the benzene ring, while the TP exhibits a negative crown just above the benzene carbon atoms, where electrophilic attack takes place. The TP calculated for the interaction of nitrobenzene with a hydride ion instead of a proton allowed analyzation of the effects of polarization on the positive EP above the N-C bond. [less ▲]

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See detailEnergy hypersurface local properties of the O2HF-1 rearrangement
Dive, Georges ULg; Dehareng, Dominique ULg; Culot, Patrick et al

in Chemical Physics Letters (1992), 195(2-3), 189-193

This work analyses a case where Murrell's proposal, stating that a second-order point must lie above a first-order one, is apparently violated. Study at the SCF-UMP2 level within the D95 + + basis set, of ... [more ▼]

This work analyses a case where Murrell's proposal, stating that a second-order point must lie above a first-order one, is apparently violated. Study at the SCF-UMP2 level within the D95 + + basis set, of one critical point of the O2HF- anion, previously proposed to be of order two by Lopez, shows the importance of the electronic correlation. The critical point associated with the (2)PI first-order ones. The present analysis reveals that this contradistinction can be explained by three unconsidered elements: the local symmetry, the electronic correlation and the internal variables description. [less ▲]

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See detailInfluence of the Counterpoise Correction on the Optimized Relativi Degrees of Freedom in the H-Bonded Complex Water-Formamide
Dehareng, Dominique ULg; Dive, Georges ULg; Ghuysen, Jean-Marie ULg

in Theoretica Chimica Acta (1992), 81(4-5), 281-290

The correction of the basis set superposition error by the counterpoise method has been investigated at the SCF level for the weak H-bonded water-formamide complex and the results have been compared with ... [more ▼]

The correction of the basis set superposition error by the counterpoise method has been investigated at the SCF level for the weak H-bonded water-formamide complex and the results have been compared with the uncorrected results at the SCF, post SCF and semi-empirical AM1 and MNDO levels. Our particular concern has been the determination of the three optimized relative degrees of freedom and the relative stability of three C(s) geometrical conformations. The conclusions are that the counterpoise correction weakly conditions the variation in the degrees of freedom and the relative stabilities of the three conformers. The correction is obviously inadequate to describe intramolecular deformation. [less ▲]

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See detailPolarization correction to the electrostatic potential at the CNDO and the ab initio level. Influence of the basis set expansion
Dehareng, Dominique ULg; Dive, Georges ULg; Ghuysen, Jean-Marie ULg

in Theoretica Chimica Acta (1991), 79(2), 141-152

The influence of the basis set on the electrostatic potential corrected for polarization has been studied for H2S, CH3SH and COHCH2SH. The position and deepness of the minima and the height of the barrier ... [more ▼]

The influence of the basis set on the electrostatic potential corrected for polarization has been studied for H2S, CH3SH and COHCH2SH. The position and deepness of the minima and the height of the barrier between symmetric minima is discussed at both the deorthogonalized CNDO/2 and ab initio levels within STO-3G, 3-21G, 4-31G, 6-31G and 6-311G basis sets. The calculation of the electrostatic potential and corrected one using CNDO deorthogonalized coefficients including 3d orbitals has been applied at the first time on sulfur-containing molecules. The influence of polarization and diffuse functions has also been analysed and the incidence of the polarization correction on the relative proton affinity in NH2(CH2)3NHCH3 and in the adenine molecule has been investigated at the CNDO and ab initio levels. At both levels, the relative proton affinity of several basic sites in the same molecule can be qualitatively expressed without inclusion of the polarization correction except in the case of substituted amines. [less ▲]

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See detailElectrostatic potential maps at the quantum chemistry level of the active sites of the serine peptidases, α-chymotrypsin and subtilisin
Lamotte-Brasseur, Josette; Dive, Georges ULg; Dehareng, Dominique ULg et al

in Journal of Theoretical Biology (1990), 145(2), 183-98

The electronic properties of the active-sites of the structurally unrelated serine peptidases, alpha-chymotrypsin and subtilisin, have been expressed in the form of three-dimensional electrostatic ... [more ▼]

The electronic properties of the active-sites of the structurally unrelated serine peptidases, alpha-chymotrypsin and subtilisin, have been expressed in the form of three-dimensional electrostatic potential maps derived from integrals calculated at the quantum chemistry level. As a consequence of the asymmetrical distribution of the secondary structures that occur within a 7 A sphere around the serine of the catalytic triad, the active sites are highly polarized entities and exhibit large dipole moments. One part of the active sites generates a nucleophilic suction-pump. Its isocontour at -10 kcal mol-1 defines an impressive, negatively-charged volume which bears a narrow channel in the immediate vicinity of the active-site serine 195 in alpha-chymotrypsin or 221 in subtilisin. In native alpha-chymotrypsin, there is a perfect complementation between this nucleophilic suction-pump and the positively-charged electrophilic hole that is generated by the backbone NH of Ser 195 and Gly 193. In subtilisin, generation of the complementing electrophilic hole requires binding of a carbonyl donor ligand and may be achieved by rotation of the side-chain amide of Asn 155 towards the backbone NH of Ser 221. Small variations in the atomic co-ordinates of alpha-chymotrypsin used for the calculations, the presence of water molecules in its active site and the occurrence of point mutations in the amino acid sequence of subtilisin have little effects on the shape and characteristics of the electrostatic potential. [less ▲]

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See detailNumerical computation of the electrostatic interaction energy between methanol and the dyad water-imidazole
Dehareng, Dominique ULg; Dive, Georges ULg; Lamotte-Brasseur, Josette ULg et al

in Theoretica Chimica Acta (1989), 76(2), 85-94

The electrostatic interaction energy between methanol and the dyad water-imidazole has been computed numerically at three levels of approximation from 3D grids of the charge density of one partner and the ... [more ▼]

The electrostatic interaction energy between methanol and the dyad water-imidazole has been computed numerically at three levels of approximation from 3D grids of the charge density of one partner and the electrostatic potential of the other. The minimum positions and energy values thus obtained compare well with those calculated analytically. The numerical procedure is especially interesting for the prediction of the stable conformers. [less ▲]

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See detailSEMICLASSICAL WAVE PACKET DYNAMICS IN NONADIABATIC PROCESSES - THE CONICAL INTERSECTION BETWEEN THE X AND A STATES OF C2H4+
Dehareng, Dominique ULg

in Chemical Physics (1988), 120(2), 261-271

Autocorrelation and probablitity functions are calculated by semiclassical wave packet dynamics for the nuclear evolution of C2H4+ in its A state, connected with the X state via a conical intersection ... [more ▼]

Autocorrelation and probablitity functions are calculated by semiclassical wave packet dynamics for the nuclear evolution of C2H4+ in its A state, connected with the X state via a conical intersection. Three distinct choices of potential energy surfaces were made: the canonic diabatic surface H22, as defined by Köppel, the adiabatic surface E2 and the Nikitin diabatic one. The wave packet is expanded in a Gaussian basis set restricted to 40 functions. The influence of the initial Gaussian width as well as the influence of freezing this width or not is studied. Taking into account the fact that this basis set is very small, one can conclude that the results are in qualitative agreement with those obtained by Köppel. The apparent discrepancy between the canonic diabatic autocorrelation function and the exact one could be explained by the existence of a dynamical condition for the choice of the diabatic potential energy surface. In the case of C2H4+(A), the behavior during the relaxation cannot be considered as essentially diabatic or adiabatic: it is intermediate. [less ▲]

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See detailNONADIABATIC UNIMOLECULAR REACTIONS .2. ISOTOPE EFFECTS ON THE KINETIC-ENERGY RELEASE
Remacle, Françoise ULg; Dehareng, Dominique ULg; Lorquet, Jean-Claude ULg

in Journal of Physical Chemistry (1988), 92(16), 4784-4787

This paper investigates the isotope effect that occurs when XOCO+ ions dissociate into XOC+ + 0 on a microsecond time scale (X = H or D). The reaction mechanism involves an electronic spin-forbidden ... [more ▼]

This paper investigates the isotope effect that occurs when XOCO+ ions dissociate into XOC+ + 0 on a microsecond time scale (X = H or D). The reaction mechanism involves an electronic spin-forbidden predissociation between a stable singlet state and a repulsive triplet. Application of the statistical equations developed in the previous paper shows that, at a given energy, the predissociation rate constant is consistently smaller for DOCO’ than for HOCO+. Therefore, the internal energy necessary to bring about dissociation of the hydrogenated compound with a given rate constant is always lower than that of the deuteriated compound by a quantity AE* which is found to be equal to ca. 0.050 eV when k = lo6 s-l and to ca 0.020 eV for k = lo3 s-1. As a result, the excess energy which is released as kinetic energy carried by the fragments is substantially greater for the deuteriated than for the hydrogenated compound. This accounts for experiments which indicate that, in the microsecond time scale, DOCO’ gives rise to a dished metastable peak whereas the corresponding signal for HOCO’ is simply Gaussian. [less ▲]

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See detailConstructing approximatively diabatic states from LCAO-SCF-CI calculations
Desouter-Lecomte, Michèle ULg; Dehareng, Dominique ULg; Lorquet, Jean-Claude ULg

in Journal of Chemical Physics (1987), 86(3), 1429-1436

We consider here two approaches which have been proposed in the literature to obtain diabatic states from ab initio calculations. First by calculating explicitely the coupling vector g which describes the ... [more ▼]

We consider here two approaches which have been proposed in the literature to obtain diabatic states from ab initio calculations. First by calculating explicitely the coupling vector g which describes the nonadiabatic interaction between the adiabatic states. Second, by some extrapolation process of the wavefunctions obtained at a particular reference point. The coupling vector is a sum of three contributions. The first two represent the the change in character of the adiabatic states in the region of nonadiabatic coupling due the variation of the CI and LCAO coefficients, whereas the third results from the translation of the atomic orbitals with the moving nuclear centers. Criteria have been given to recognize when it is possible to transform a set of CI wave functions into a pair of useful diabatic states. A particularly favorable situation is obtained when the interacting electronic states are doubly excited with respect to each other. Within the two-states approximation, the first term, depending on the CI coefficients, is strictly irrotational and never gives rise to problems. One can expect situations where it is also true for the second term depending on the LCAO coefficients. However, the third term of the coupling can never be described as a rotation of two diabatic functions. Nevertheless, the latter contribution can frequently be neglected, at least when the coupling is strong. The theory of the electron transfer factors (ETF's) provides further insight into the problem and confirm our conclusions. [less ▲]

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See detailAN ABINITIO STUDY OF THE ISOMERIZATION AND FRAGMENTATION OF CHO2+ IONS - AN EXAMPLE OF SPIN-CONTROLLED REACTIONS
Remacle, Françoise ULg; Petitjean, Serge; Dehareng, Dominique ULg et al

in International Journal of Mass Spectrometry and Ion Processes (1987), 77(2-3), 187-201

[CHO2+] ions exist in two isomeric forms, a quasi-linear carboxylic structure, OCOH+ (I), and a formate structure, O(CH)O+ (II). The latter is known to isomerise into the former with a low rate constant ... [more ▼]

[CHO2+] ions exist in two isomeric forms, a quasi-linear carboxylic structure, OCOH+ (I), and a formate structure, O(CH)O+ (II). The latter is known to isomerise into the former with a low rate constant (about 105 s−1). Configuration interaction ab initio calculations reveal that the ion can exist in three low-lying electronic states of different multiplicity and symmetry species, a singlet (Image 1A′) and two triplets (ã3A′ and Image 3A′'). The potential energy surfaces cross so that the nature of the lowest state varies as a function of the nuclear geometry. The singlet surface (Image 1A′) has its deepest minimum for structure I and a subsidiary minimum for structure II. The situation is reversed for the ã3A′ state which has its deepest minimum for structure II and which exhibits a shallow minimum for structure I. Thus, at low energies, the carboxylic and formate ions are respectively in a singlet and in a triplet state. These ions lose an oxygen atom on a microsecond time scale by a composite mechanism which is subject to a large isotope effect. One of the components of the metastable peak corresponds to reaction OCOH+(1A') -> O(CH)O+ (3A') -> HCO+ + O giving rise to a small kinetic energy release. The second component is due to a spin-orbit controlled direct predissociation process, viz. OCOH+ (1A') -> OCOH+ (3A') -> HOC+ + O. The probability of surface hopping varies as a function of the internal energy between 0 and a maximum value of ca. 0.008. The corresponding kinetic energy release is expected to be larger for the deuterated than for the hydrogenated compound. Thus, the two components are resolved in the deuterated compound, but hardly distinguishable in the hydrogenated species. [less ▲]

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