Classical dynamics of triatomic systems. I. Dynamics of energized harmonic molecules. II. Dynamics of energized anharmonic molecules. III. The H + DX reactions

Abstract

Part I. Dynamics of Energized Harmonic Molecules: The classical equations of motion of some bent triatomic harmonic molecular models are integrated numerically to investigate the assumptions underlying contemporary theories of unimolecular reaction rates. The small vibration and weak coupling approximations are shown to be inadequate for energies near dissociation, but reaction frequencies, based upon a modification of the former approximation, are seen to be in good agreement with the model's actual reaction frequencies. The effects of rotation upon intramolecular energy exchange are shown to be non-negligible. The effects of bond anharmonicity were not included in this paper. Part II. Dynamics of Energized Anharmonic Molecules: The classical equations of motion of two anharmonic bent triatomic molecular models are integrated numerically. It is found that at dissociative energies, the intramolecular energy transfer rate is the frequency with which any two bonds compress. The normal mode description of the motion is observed to be entirely inadequate. Molecular lifetimes are shown to be unstable to small perturbations in the initial conditions for the molecular trajectory. This instability may imply gross differences in the classical and quantal lifetimes of energized molecules. Part III. The H + DX Reactions: A Sato surface, free of spurious wells, is proposed for the reaction H + DBr. The abstraction fraction, the ratio of abstraction to total reaction rate, is shown to have similar large temperature dependence from activated complex theory that is found from classical trajectory results. The latter yield broad product energy distributions and reaction cross sections which peak (at ~ 1 eV relative energies) at 3 and 13 aO2 for abstraction and exchange, respectively.