4 research outputs found
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
Approches statisticodynamiques de la réactivité chimique
La dissociation unimolĂ©culaire de systĂšmes chimiques faiblement liĂ©s (molĂ©cules de van der Waals, HeBr2, NeBr2, ArBr2) et covalents (NCO, CH2CO) est Ă©tudiĂ©e au moyen de la mĂ©thode des trajectoires classiques et dâune approche statistique basĂ©e sur la thĂ©orie de lâĂ©tat de transition. Dâune part, lâapport de la procĂ©dure de pondĂ©ration gaussienne appliquĂ©e Ă la dĂ©termination de distribution ro-vibrationnelles et dâĂ©nergie de translation, est illustrĂ©e. Dâautre part, une transformation des coordonnĂ©es angle-action aux coordonnĂ©es cartĂ©siennes, dans le cas gĂ©nĂ©ral de fragments polyatomiques, ainsi que quâune correction quasi-classique permettant dâincorporer la structure rotationnelle aux distributions rĂ©solues vibrationnellement, sont dĂ©veloppĂ©es. Sur la base de ces dĂ©veloppements, une mĂ©thodologie applicable aux processus polyatomiques indirects conduisant Ă une rĂ©solution ro-vibrationnelle complĂšte sans nĂ©cessiter de procĂ©dures de pondĂ©ration ou de binning, est prĂ©sentĂ©e.The quasi-classical trajectory method and statistical assumptions from the transition state theory are employed in the investigation of the unimolecular dissociation of weakly (van der Waals aggregates, i.e. HeBr2, NeBr2, ArBr2) and conventionally bound molecular systems (NCO, CH2CO). The capabilities of the Gaussian weighting procedure are illustrated through the reproduction of ro-vibrational and translational energy distributions. A transformation from angle-action variables to Cartesian coordinates is derived for the general case of polyatomic fragments. An alternative methodology is developed to study indirect polyatomic processes which provides complete ro-vibrational resolution while effectively avoids any binning or weighting procedure. The new algorithm is based on the transformation previously derived and an approximate formula developed to incorporate the rotational structures on the vibrationally-resolved quasi-classical distributionsEl mĂ©todo de trayectorias cuasi-clasicas e hipotesis estadisticas de la teoria del estado de transicion, son empleados en la investigacion de la disociacion unimolecular de sistemas dĂ©bil (agregados de van der Waals, i.e. HeBr2, NeBr2, ArBr2) y convencionalmente enlazados (NCO, CH2CO). Se demuestran las potencialidades del procedimiento de ponderacion gaussiana para la reproduccion de distribuciones ro-vibracionales y de energia de traslacion, en comparacion con las obtenidas por los mĂ©todos convencionales. Son desarrolladas la transformacion desde variables angulares y de accion a coordenadas cartesianas para el caso general de fragmentos poliatomicos, asi como un conjunto de expresiones cuasi-clasicas para incorporar estruturas rotacionales en las distribuciones resueltas vibracionalmente. Sobre la base de estos desarrollos, se demuestra y aplica una nueva metodologia para estudiar procesos poliatomicos indirectos con la que resulta posible obtener distribuciones tĂ©oricas con resolucion ro-vibracional total, evitando el uso de mĂ©todos de binning o ponderaciones
Approches statisticodynamiques de la réactivité chimique
La dissociation unimolĂ©culaire de systĂšmes chimiques faiblement liĂ©s (molĂ©cules de van der Waals, HeBr2, NeBr2, ArBr2) et covalents (NCO, CH2CO) est Ă©tudiĂ©e au moyen de la mĂ©thode des trajectoires classiques et dâune approche statistique basĂ©e sur la thĂ©orie de lâĂ©tat de transition. Dâune part, lâapport de la procĂ©dure de pondĂ©ration gaussienne appliquĂ©e Ă la dĂ©termination de distribution ro-vibrationnelles et dâĂ©nergie de translation, est illustrĂ©e. Dâautre part, une transformation des coordonnĂ©es angle-action aux coordonnĂ©es cartĂ©siennes, dans le cas gĂ©nĂ©ral de fragments polyatomiques, ainsi que quâune correction quasi-classique permettant dâincorporer la structure rotationnelle aux distributions rĂ©solues vibrationnellement, sont dĂ©veloppĂ©es. Sur la base de ces dĂ©veloppements, une mĂ©thodologie applicable aux processus polyatomiques indirects conduisant Ă une rĂ©solution ro-vibrationnelle complĂšte sans nĂ©cessiter de procĂ©dures de pondĂ©ration ou de binning, est prĂ©sentĂ©e.The quasi-classical trajectory method and statistical assumptions from the transition state theory are employed in the investigation of the unimolecular dissociation of weakly (van der Waals aggregates, i.e. HeBr2, NeBr2, ArBr2) and conventionally bound molecular systems (NCO, CH2CO). The capabilities of the Gaussian weighting procedure are illustrated through the reproduction of ro-vibrational and translational energy distributions. A transformation from angle-action variables to Cartesian coordinates is derived for the general case of polyatomic fragments. An alternative methodology is developed to study indirect polyatomic processes which provides complete ro-vibrational resolution while effectively avoids any binning or weighting procedure. The new algorithm is based on the transformation previously derived and an approximate formula developed to incorporate the rotational structures on the vibrationally-resolved quasi-classical distribution