Studies of a model of hydrogen recombination

Abstract

A Morse oscillator model for recombination of hydrogen and its isotopes was investigated computationally. The model is very similar to one recently studied by Pritchard and co-workers. The aims of the study were the test of certain approximations and the determination of the range of validity of the model. It was found that at low temperatures the steady state approximation is an increasingly accurate and increasingly convenient approximation. A way of estimating the error arising from this approximation was proposed. Other approximations which were tested gave unsatisfactory results. The rate constant vs. temperature curve for the model does not agree well with the experimental curve for hydrogen in argon except insofar as it reproduces the observed levelling-off at high temperatures. For the model this result may be ascribed to increasing relative rates for multiquantum transitions among the levels of the diatom. The model does give the experimentally observed ratios of the rate constants for H-and D-atom recombination. This result indicates that the important factor in determining the isotope ratio is the effect of mass change on the density of states rather than its effect on the collision dynamics.NEIL S. SNIDER. Can. J. Chem. 55, 3464 (1977). On a etudie, a I'aide d'un calculateur, la recombinaison de I'hydrogene et de ses isotopes en prenant comme modele l'oscillateur de Morse. LC modtle est tres proche de celui rtcemment Btudie par Pritchard et ses collaborateurs. LC but de cette etude est de verifier certaines approximations et de determiner la zone oh le modele est valable. I1 apparait qu'a basse temperature I'approximation de 1'Ctat stationnaire est de plus en plus exacte et convenable. On propose une methode d'haluation de I'erreur sur cette approximation. Plusieurs autres approximations n'ont pas donne de bons resultats. La courbe de la constante de vitesse vs. la temptrature pour ce modde ne correspondent pas bien a la courbe expCrimentale pour l'hydrogtne dans I'argon. On peut utiliser cette courbe en autant qu'elle reproduit le palier observe a haute tempQature. LC resultat obtenu pour ce modele peut ttre attribut a l'accroissement des vitesses relatives de transitions multiquantiques parmi les niveaux du diatome. D'ailleurs, le modtle reproduit les rapports qui sont observes expCrimentalen~ent pour les constantes de vitesse pour la combinaison des atomes H et D. Ce resultat suggere que le phknomtne majeur dans la determination du rapport isotopique est I'effet de la variation de masse sur la densitt des ttats plut8t que son effet sur la dynamique des collisions.[Traduit par le journal]

Bound complex and triple collision mechanisms for diatom dissociation and recombination

“…If the A-M attractive forces are strong, where p is given by theless, in those cases for which calculations are With O given by [6] and coordinates given by [7], : reported here, the A-M attractive forces are weak.…”

“…As the first step in the evaluation of these integrals, explicit coordinates are chosen. These are R, the distance from M to the center of mass of A, and r, the A-A distance, both conveniently mass weighted, In [7], rAA is the A-A distance, rAM is the distance between M and the nearest A, and b is given by where m, and mM are the masses of the designated atoms. In terms of these coordinates the Hamiltonian for the vibration of isolated A, is given by i tion seems physically reasonable in those cases for and the total Hamiltonian is given by !…”

“…The way in which X*, n, and E, are calculated is described in ref. 7. At low temperatures one can safely make the approximation where (in this section only) r denotes gamma function.…”

“…simple method for extending collinear results for k, In the region for which &nt is less than D7 it is the to three dimensions (7). The extended results can be surface along whichf is zero.…”

A simple model of rotational effects in thermal decomposition

“…This can be studied by solving a rather complicated master equation for the population distribution, and has been attempted only for a few simple cases. Detailed numerical studies of H 2 have been carried out [7][8][9] and some attempts have been made to simplify the two-dimensional (vibration-rotation) master equation to the point where it can be applied to the decomposition of polyatomic species [10,11]. In all of this, there is still room for a qualitative discussion of non-equilibrium effects, since even such a simple question as to whether rotational effects necessarily increase the non-equilibrium behaviour of the populations, or decrease it, has not yet been fully answered.…”