Jean-Claude Rayez

University of Bordeaux, Burdeos, Aquitaine, France

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Publications (44)125.28 Total impact

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    ABSTRACT: The yield of 1- and 2-butyl nitrates in the gas-phase reactions of NO with n-C4H9O2 and sec-C4H9O2, obtained from the reaction of F-atoms with n-butane in the presence of O2, was determined over the pressure range 100 - 600 Torr at 298 K using a high-pressure turbulent flow reactor coupled with a chemical ionization quadrupole mass-spectrometer. The yield of butyl nitrates was found to increase linearly with pressure from about 3% at 100 Torr to about 8% at 600 Torr. The results obtained are compared with the available data concerning nitrate formation from NO reaction with other small alkyl peroxy radicals. These results are also discussed through the topology of the lowest potential energy surface mainly obtained from DFT(B3LYP/aug-cc-pVDZ) calculations of the RO2 + NO reaction paths. The formation of alkyl nitrates, due essentially to collision processes, is analyzed through a model which points out the pertinent physical parameters of this system.
    The Journal of Physical Chemistry A 11/2014; 119(19). DOI:10.1021/jp509427x · 2.78 Impact Factor
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    ABSTRACT: A flash photolysis-resonance fluorescence (FP-RF) system was used to study the p-cymene (PC) + OH reaction at temperatures between 299 and 349 K in helium. Triexponential functions were fitted to groups of observed OH decay curves according to a model considering a reversible addition to form two adducts as thermolabile reservoirs of OH. Compared to Part 1 of this paper, consideration of a second adduct strongly improved the fits to our measurements, and the rate constants for the major pathways were optimized between 299 and 349 K. The Arrhenius expression for the rate constant of the sum of OH addition and H-atom abstraction pathways was found to be kOH = 1.9 × 10(-12) exp[(610 ± 210) K/T] cm(3) s(-1). Rate constants of unimolecular decomposition reactions of the adducts were similar to other aromatic compounds with the following Arrhenius expressions: 1 × 10(12) exp[(-7600 ± 800) K/T] s(-1) for adduct 1 and 4 × 10(11) exp[(-8000 ± 300) K/T] s(-1) for adduct 2. Adduct yields increased and decreased with temperature for adduct 1 and 2, respectively, but were similar (∼0.4) around room temperature. Equilibrium constants yielded values for reaction enthalpies and entropies of adduct formations. While for one adduct reasonable agreement was obtained with theoretical predictions, there were significant deviations for the other adduct. This indicates the presence of more than two adduct isomers that were not accounted for in the reaction model. Quantum chemical calculations (DFT M06-2X/6-31G(d,p)) and RRKM kinetics were employed with the aim of clarifying the mechanism of the OH addition to PC. These calculations show that formation of adducts with OH in ortho positions to the isopropyl and methyl substituents is predominant (55% and 24%) to those with OH in ipso positions (21% and 3%). A large fraction (>90%) of the ipso-C3H7 adduct is predicted to react by dealkylation forming p-cresol (in the absence of oxygen) and isopropyl radicals. These theoretical results agree well with the interpretation of the experimental results showing that the two ortho adducts (which appeared as OH reservoirs in the experiment) have been observed.
    Physical Chemistry Chemical Physics 07/2014; 16(32). DOI:10.1039/c4cp02073a · 4.20 Impact Factor
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    ABSTRACT: The density functional theory with the BH&HLYP functional has been used in this work to clarify discrepancies found in the literature about the effect of the increasing carbon chain on the reactivity of trans-2-alkenals from acrolein (C3) to trans-2-octenal (C8) with nitrate radical. In this work, it was found that (i) the alkyl chain length of the unsaturated aldehydes has little or no influence on the NO3 reaction rate coefficients (ii) the abstraction of the aldehydic hydrogen from the alkenal is always dominant (83% for trans-2-butanal to trans-2-octenal). The addition channel, which mainly concerns the β addition, has a small influence (17% of the total reaction for the whole series). These results are in good agreement with the experimental studies performed by Zhao et al. in 2011 and by Kerdouci et al. in 2012. All these findings will be useful to complete or improve structure-activity relationships developed to predict the reactivity of NO3 radicals with organic compounds.
    The Journal of Physical Chemistry A 07/2014; 118(28). DOI:10.1021/jp503619d · 2.78 Impact Factor
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    ABSTRACT: First-principle calculations are performed to characterize the NO adsorption on large carbonaceous clusters modeling the surface of soot. Adsorption on the face and on the edges of perfect and defective clusters is considered in the calculations. It is shown that the first situation corresponds to physisorption and requires taking into account long-range dispersion interactions in the calculations. In contrast, interaction of NO with the unsaturated edge of a defective cluster leads preferentially to a C-N rather than to a C-O chemical binding. This indicates that soot may be an efficient sink for NO in the Troposphere only if it contains a high number of unsaturated carbon atoms. From a more fundamental point of view, this study also clearly evidences that quantum calculations have to be carefully conducted when considering the interaction between radical species and carbonaceous surfaces. Problems encountered with the choice of the functional used in density functional theory approaches as well as with the size of the basis set, spin multiplicity, and spin contamination have to be systematically addressed before any relevant conclusion can be drawn.
    The Journal of Physical Chemistry A 02/2014; 118(8). DOI:10.1021/jp412217q · 2.78 Impact Factor
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    ABSTRACT: Aromatic hydrocarbons are important components of polluted ambient air. The reaction of OH radicals with HexaMethylBenzene (HMB) is a prototype system to study ipso addition leading eventually to dealkylation. We have investigated the OH + HMB and OD + HMB reactions between 323 and 433 K using a discharge fast-flow reactor coupled to a time-of-flight mass spectrometer with single-photon VUV photoionization (10.54 eV). The H atom abstraction channel has been found to be equal to (13.7 +/- 4.4) % at 330 K leading to (11.1 +/- 3.6) % at 298 K, higher than predicted by commonly-used structure-reactivity relationships. The back dissociation rate constant has also been measured and has been found to be smaller than the rate of other aromatic hydrocarbons, in good agreement with density functional theoretical calculations. The dealkylation channel, leading to PentaMethylPhenol (PMP) + CH3, is always found to be the minor channel, estimated inferior to 2% at 298K.
    The Journal of Physical Chemistry A 11/2012; 116(50). DOI:10.1021/jp307568c · 2.78 Impact Factor
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    ABSTRACT: A large part of biphenyl structures in lignin are etherified by α- and β-carbons of another phenylpropane unit to give an eight-member ring called dibenzodioxocin. The behavior of a phenolic dibenzodioxocin lignin model, 4-(4,9-dimethoxy-2,11-n-dipropyl-6,7-dihydro-5,8-dioxa-dibenzo[a,c]cycloocten-6-yl)-2-methoxyphenol (DBDOH, 1), was studied by different mass spectrometry and thermal methods, leading to the conclusion that dibenzodioxocins are thermally unstable products. Both semi-empirical and density functional theory quantum calculations show that both C–O bonds, which connect the biphenyl part of the dibenzodioxocin molecule to the phenolic group, can be broken under increasing temperature. However, they do not play the same role since their dissociation occurs through different barrier heights. The C–O bond directly connected to the phenolic group (α–O-4) will dissociate first since its barrier energy for scission is lower than the other one (β–O-4), by roughly 12 kcal mol–1 (≈50 kJ mol−1). This conclusion is likely applicable to thermal degradation of DBDO units in lignin polymer.
    Wood Science and Technology 01/2012; 47(1). DOI:10.1007/s00226-012-0478-7 · 1.87 Impact Factor
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    ABSTRACT: Quantum calculations are used to study the interaction of water molecules with carbonaceous clusters containing one single carbon atom vacancy. This is a simple but realistic way to model the active surfaces found in soot emitted by aircrafts. Prior to water adsorption, the atomic vacancy is oxidised by an approaching oxygen molecule, which is also likely to occur behind planes. The results of the calculations show that this oxidation process results in the formation of one ketone-like site and one epoxide-like site around the atomic vacancy. These sites may act as nucleation centers for water molecules, which are, however, physisorbed on the oxidized surface, leading to very weak charge transfer with the surface. Although less attractive for water than, for instance, a carboxyl-like site, the ketone-like site can also participate in the hydrophilic behavior of soot primary particles. In contrast, the epoxide-like site formed around the vacancy shows a very low affinity for water molecules.
    ChemPhysChem 12/2010; 11(18):4088-96. DOI:10.1002/cphc.201000364 · 3.36 Impact Factor
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    ABSTRACT: First-principle calculations are used to study the interaction of water molecules with carbonaceous clusters containing single carbon atom vacancy, similar to those which may be found in soot nanoparticles. It is shown that the dissociative adsorption of one water molecule at the vacancy site may lead to the formation of a “ketone-like” structure which can then act as a nucleation center for additional water molecules. Such a mechanism can thus participate in the hydrophilic behavior of soot primary particles although it appears less favorable than water nucleation around more hydrophilic sites such as carboxyl or hydroxyl groups.
    Surface Science 09/2010; 604(19-20):1666-1673. DOI:10.1016/j.susc.2010.06.011 · 1.87 Impact Factor
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    ABSTRACT: An alternative methodology to investigate indirect polyatomic processes with quasi-classical trajectories is proposed, which effectively avoids any binning or weighting procedure while provides rovibrational resolution. Initial classical states are started in terms of angle-action variables to closely match the quantum experimental conditions and later transformed into Cartesian coordinates, following an algorithm very recently published [J. Chem. Phys. 2009, 130, 114103]. Trajectories are then propagated using the 'association' picture, i.e. an inverse dynamics simulation in the spirit of the exit-channel corrected phase space theory of Hamilton and Brumer [J. Chem. Phys. 1985, 82, 595], which is shown to be particularly convenient. Finally, an approximate quasi-classical formula is provided which under general conditions can be used to add possible rotational structures into the vibrationally-resolved quasi-classical distributions. To introduce the method and illustrate its capabilities, correlated translational energy distributions from recent experiments in the photo-dissociation of ketene at 308 nm [J. Chem. Phys. 2006, 124, 014303] are investigated. Quite generally, the overall theoretical algorithm reduces the total number of trajectories to integrate and allows for fully theoretical predictions of experiments on polyatomics.
    Physical Chemistry Chemical Physics 01/2010; 12(1):115-22. DOI:10.1039/b917292k · 4.20 Impact Factor
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    ABSTRACT: The influence of water vapor on the production of nitric acid in the gas-phase HO(2) + NO reaction was determined at 298 K and 200 Torr using a high-pressure turbulent flow reactor coupled with a chemical ionization mass spectrometer. The yield of HNO(3) was found to increase linearly with the increase of water concentration reaching an enhancement factor of about 8 at [H(2)O] = 4 x 10(17) molecules cm(-3) ( approximately 50% relative humidity). A rate constant value k(1bw) = 6 x 10(-13) cm(3) molecule(-1) s(-1) was derived for the reaction involving the HO(2)xH(2)O complex: HO(2)xH(2)O + NO --> HNO(3) (1bw), assuming that the water enhancement is due to this reaction. k(1bw) is approximately 40 times higher than the rate constant of the reaction HO(2) + NO --> HNO(3) (1b), at the same temperature and pressure. The experimental findings are corroborated by density functional theory (DFT) calculations performed on the H(2)O/HO(2)/NO system. The significance of this result for atmospheric chemistry and chemical amplifier instruments is briefly discussed. An appendix containing a detailed consideration of the possible contribution from the surface reactions in our previous studies of the title reaction and in the present one is included.
    The Journal of Physical Chemistry A 09/2009; 113(42):11327-42. DOI:10.1021/jp811428p · 2.78 Impact Factor
  • Jean-Claude Rayez, Robert Lesclaux
    Angewandte Chemie 06/2009; 121(28):5177-5177. DOI:10.1002/ange.200901202
  • The Journal of Chemical Physics 01/2009; 130(4):9901-. DOI:10.1063/1.3062861 · 3.12 Impact Factor
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    ABSTRACT: In this paper, molecular dynamic simulations are used to study the adsorption of water molecules on partially oxidized graphite surfaces containing COOH and OH sites. More specially, the competition between the OH and COOH sites with respect to water adsorption is characterized at three different temperatures (200, 250 and 300 K). The simulations show a strong preferential clustering of the water molecules around the COOH sites irrespective of the temperature. The present results also show that the OH sites can influence the water adsorption process at high temperature, if their local density on the surface is sufficiently large. In this situation, the dynamics of the adsorption process is shown to depend on the distribution of these OH sites on the surface. These results give insights into the water adsorption mechanisms on oxidized graphite surfaces constituting, for example, black carbons or soot particles emitted by aircraft.
    Physical Chemistry Chemical Physics 01/2009; 10(46):6998-7009. DOI:10.1039/b811126j · 4.20 Impact Factor
  • Aurelie Perrier, Laurent Bonnet, Jean-Claude Rayez
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    ABSTRACT: Transition state theory: a reaction dynamics tool applied to gas-surface reactions Recombinative desorption of molecules from a metal surface is a fundamental step in heterogeneous catalytic reactions. Understanding this elementary mechanism can bring precious information on both the dynamics and the kinetics of gas-surface reactions. The aim of this work was to combine classical trajectory calculations and transition state theory based approaches to study the dynamics of molecular associative desorption. We were particularly interested in the description of state distributions in the products of associative molecular desorption. For late barrier processes such as H(2)/Pt(111), energy transfers between vibrational, rotational and translational motions of the departing molecule are too weak to alter its state distributions. Accordingly, transition state theory gives a straightforward description of final state distributions. On the opposite, for early barrier processes, such as H(2)/Cu(111), strong energy transfers occur in the exit channel. Therefore we must apply the so-called "statistico-dynamical approach". This method is partly based upon transition state theory and takes into account energy transfers which occur between rotational and translational motions en route to the gas phase. Therefore, the statistico-dynamical approach gives a description of rotational state distributions of desorbed molecules. For both processes under investigation, statistical methods were found to be in very good agreement with both classical trajectory calculations and experimental results.
    Molecular Science 01/2009; DOI:10.3175/molsci.3.A0029
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    ABSTRACT: Silylboranes with aromatic substituents linked to boron and silicon exhibit an unexpected absorption band in the UV–Vis spectral region. When polar groups were introduced, a marked solvatochromic effect was observed in their fluorescence emission spectra, revealing a strong excited state dipole moment. Semi-empirical MNDO/d and AM1 calculations showed that, upon UV excitation, the polarity of the Si–B bond increased and the aromatic π-electrons migrated toward the Si–B bond, consistent with experimental observations.
    Journal of Organometallic Chemistry 07/2008; 693(15):2592-2596. DOI:10.1016/j.jorganchem.2008.04.031 · 2.17 Impact Factor
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    ABSTRACT: The possible existence of a complex-forming pathway for the H+O(2) reaction has been investigated by means of both quantum mechanical and statistical techniques. Reaction probabilities, integral cross sections, and differential cross sections have been obtained with a statistical quantum method and the mean potential phase space theory. The statistical predictions are compared to exact results calculated by means of time dependent wave packet methods and a previously reported time independent exact quantum mechanical approach using the double many-body expansion (DMBE IV) potential energy surface (PES) [Pastrana et al., J. Phys. Chem. 94, 8073 (1990)] and the recently developed surface (denoted XXZLG) by Xu et al. [J. Chem. Phys. 122, 244305 (2005)]. The statistical approaches are found to reproduce only some of the exact total reaction probabilities for low total angular momenta obtained with the DMBE IV PES and some of the cross sections calculated at energy values close to the reaction threshold for the XXZLG surface. Serious discrepancies with the exact integral cross sections at higher energy put into question the possible statistical nature of the title reaction. However, at a collision energy of 1.6 eV, statistical rotationally resolved cross sections managed to reproduce the experimental cross sections for the H+O(2)(v=0,j=1)-->OH(v(')=1,j('))+O process reasonably well.
    The Journal of Chemical Physics 06/2008; 128(24):244308. DOI:10.1063/1.2944246 · 3.12 Impact Factor
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    ABSTRACT: The dynamics of the singlet channel of the Si+O2→SiO+O reaction is investigated by means of quasiclassical trajectory (QCT) calculations and two statistical based methods, the statistical quantum method (SQM) and a semiclassical version of phase space theory (PST). The dynamics calculations have been performed on the ground 1A′ potential energy surface of Dayou and Spielfiedel [J. Chem. Phys. 119, 4237 (2003)] for a wide range of collision energies (Ec = 5–400 meV) and initial O2 rotational states (j = 1–13). The overall dynamics is found to be highly sensitive to the selected initial conditions of the reaction, the increase in either the collisional energy or the O2 rotational excitation giving rise to a continuous transition from a direct abstraction mechanism to an indirect insertion mechanism. The product state properties associated with a given collision energy of 135 meV and low rotational excitation of O2 are found to be consistent with the inverted SiO vibrational state distribution observed in a recent experiment. The SQM and PST statistical approaches, especially designed to deal with complex-forming reactions, provide an accurate description of the QCT total integral cross sections and opacity functions for all cases studied. The ability of such statistical treatments in providing reliable product state properties for a reaction dominated by a competition between abstraction and insertion pathways is carefully examined, and it is shown that a valuable information can be extracted over a wide range of selected initial conditions.
    The Journal of Chemical Physics 05/2008; 128(17):174307-174307-16. DOI:10.1063/1.2913156 · 3.12 Impact Factor
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    ABSTRACT: First quasiclassical trajectory calculations have been carried out for the C(3P)+OH(X 2Pi)-->CO(X 1Sigma+)+H(2S) reaction using a recent ab initio potential energy surface for the ground electronic state, X 2A', of HCO/COH. Total and state-specific integral cross sections have been determined for a wide range of collision energies (0.001-1 eV). Then, thermal and state-specific rate constants have been calculated in the 1-500 K temperature range. The thermal rate constant varies from 1.78x10(-10) cm3 s-1 at 1 K down to 5.96x10(-11) cm3 s-1 at 500 K with a maximum value of 3.39x10(-10) cm3 s-1 obtained at 7 K. Cross sections and rate constants are found to be almost independent of the rovibrational state of OH.
    The Journal of Chemical Physics 05/2007; 126(18):184308. DOI:10.1063/1.2731788 · 3.12 Impact Factor
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    ABSTRACT: For gas-phase chemical reactions like OH + HCl -> H2O + Cl, which involves a relatively deep pre-barrier van der Waals well, quasi-classical trajectory calculations showed that unexpected reaction pathways involving strong reorientation of the reagents may be clearly evidenced by controlling the spatial orientation of both reagent molecules. In such a case, the venerable notion of cone of acceptance does not suffice, on its own, to rationalize steric effects.
    Bulletin of the Chemical Society of Japan 04/2007; 80(4):707-710. DOI:10.1246/bcsj.80.707 · 2.22 Impact Factor
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    ABSTRACT: The kinetics and the mechanism of the reaction CH(3)C(O)O(2)+ HO(2) were reinvestigated at room temperature using two complementary approaches: one experimental, using flash photolysis/UV absorption technique and one theoretical, with quantum chemistry calculations performed using the density functional theory (DFT) method with the three-parameter hybrid functional B3LYP associated with the 6-31G(d,p) basis set. According to a recent paper reported by Hasson et al., [J. Phys. Chem., 2004, 108, 5979-5989] this reaction may proceed by three different channels: CH(3)C(O)O(2)+ HO(2)--> CH(3)C(O)OOH + O(2) (1a); CH(3)C(O)O(2)+ HO(2)--> CH(3)C(O)OH + O(3) (1b); CH(3)C(O)O(2)+ HO(2)--> CH(3)C(O)O + OH + O(2) (1c). In experiments, CH(3)C(O)O(2) and HO(2) radicals were generated using Cl-initiated oxidation of acetaldehyde and methanol, respectively, in the presence of oxygen. The addition of amounts of benzene in the system, forming hydroxycyclohexadienyl radicals in the presence of OH, allowed us to answer that channel (1c) is <10%. The rate constant k(1) of reaction (1) has been finally measured at (1.50 +/- 0.08) x 10(-11) cm(3) molecule(-1) s(-1) at 298 K, after having considered the combination of all the possible values for the branching ratios k(1a)/k(1,)k(1b)/k(1,)k(1c)/k(1) and has been compared to previous measurements. The branching ratio k(1b)/k(1), determined by measuring ozone in situ, was found to be equal to (20 +/- 1)%, a value consistent with the previous values reported in the literature. DFT calculations show that channel (1c) is also of minor importance: it was deduced unambiguously that the formation of CH(3)C(O)OOH + O(2) (X (3)Sigma(-)(g)) is the dominant product channel, followed by the second channel (1b) leading to CH(3)C(O)OH and singlet O(3) and, much less importantly, channel (1c) which corresponds to OH formation. These conclusions give a reliable explanation of the experimental observations of this work. In conclusion, the present study demonstrates that the CH(3)C(O)O(2)+ HO(2) is still predominantly a radical chain termination reaction in the tropospheric ozone chain formation processes.
    Physical Chemistry Chemical Physics 06/2006; 8(18):2163-71. DOI:10.1039/b518321a · 4.20 Impact Factor