Study of the H+O2 reaction by means of quantum mechanical and statistical approaches: The dynamics on two different potential energy surfaces

The possible existence of a complex-forming pathway for the H+O2 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+O2(v=0,j=1)-->OH(v[prime]=1,j[prime])+O process reasonably well. ©2008 American Institute of Physic

Semiclassical statistico-dynamical description of polyatomic photo-dissociations: State-resolved distributions

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. 130, 114103 (2009)]. 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. 82, 595 (1985)], 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. 124, 014303 (2006)] 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.Comment: 10 pages, 3 figures, submitted to Phys. Chem. Chem. Phys; v2: corrects Fig. 3 and its discussio

Etudes expérimentale et théorique ab initio de la réaction des atomes de fluor avec les halogénométhanes de type CHCl3-xFx (x = 0, 1, 2 ou 3)

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Contribution théorique à la compréhension des mécanismes d'oxydation de quelques composés aromatiques dans la troposphère (benzène, toluène, phénol)

Comme tous les composés organiques volatils (COV), les composés aromatiques participent à l'accroissement de la production d'ozone troposphérique. Cette production, néfaste pour la planète et les êtres vivants, a été multipliée par quatre depuis le début du XXème siècle en raison du développement des activités anthropiques. Malgré l'importance de ce problème, les mécanismes d'oxydation de ces composés ne sont ps encore clairement compris. En outre, la difficulté des études expérimentales rend indispensable les approches théoriques. L'étude systématique des différents chemins possibles au cours de l'oxydation de trois composés aromatiques (benzène, toluène, phénol) a permis de déterminer les voies réactionnelles prépondérantes et de proposer un mécanisme pour les premières étapes de leur oxydation dans les conditions troposphériques cohérent avec l'ensemble des données expérimentales disponibles.Like all volatile organic compounds (VOC), aromatic compounds contribute to the increase of the tropospheric ozone production. Due to the increase of anhropic activites, this production, harmful for the Earth and for living creatures, has been multiplied by four since the beginning of the XXst century. In spite of the importance of this topical issue, the undestanding of oxidation mechanism of these compounds is still an open question. Besides, the difficulty of experimental studies makes theoretical approaches essential. Systematic study of possible pathways on the oxidation of three aromatic compounds (benzene, toluene, phenol) allows us to determine predominant reactional routes and to propose a mechanism for the first steps of their oxidation under trophospheric conditions consistent with all experimental data available.BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

Contribution théorique à la mise en évidence de relations "structure-réactivité" dans des radicaux d'intérêt atmosphérique

BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

A theoretical characterization of the interaction of water with oxidized carbonaceous clusters

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