Chaos and resonances in the classical scattering of a positron by a model diatomic molecule.

PURPOSE: A recently proposed model potential to study quantum scattering of a positron from a hydrogen molecule is used to solve the Hamilton equations for scattering trajectories. In the present classical description, the positron can transfer energy to the vibrational mode of the molecule, remaining trapped for a while before escaping to infinity. Such vibrational resonances may correspond to trajectories which are embedded in phase-space regions of chaotic scattering.

Quasi-Classical Trajectory Study of NH(3∑-) + NH(3∑-) Reactive Collisions.

A full-dimension quasi-classical trajectory study of collisions between two NH radicals is presented. Interatomic interactions are represented by a previously reported global six-dimensional potential energy surface for singlet electronic state of the N2H2 system. This study suggests that the formation of N2 from the collision of two NH radicals may occur via a one-step (NH + NH → N2 + H + H) or two-step (NH + NH → N2H + H → N2 + H + H) microscopic reaction mechanism. A fast vibrational energy redistribution is observed in the four-body complex in the latter mechanism. Excitation functions are presented and discussed. A variant of the vibrational energy quantum mechanical threshold method was used to correct the zero-point energy leakage in the classical calculations. The influence of reactant's rotational and vibrational energy on reactivity was investigated by state-specific calculations with one or both reactants excited. Reaction rate constants for the ground and some rotationally excited states are presented using an Arrhenius-Kooij-like functional form.