Dynamics of ion-molecule recombination IV. Li + + (CH 3) 2O association

Abstract

Trajectories are used to study the dynamics of Li + + (CH 3) 2O association. The criterion for association in the trajectories is the formation of a long-lived vibrationally/rotationally excited Li + [(CH 3) 2O] ∗ association complex with multiple inner turning points in the Li + + (CH 3) 2O relative distance. Primary association cross sections are determined as a function of the initial relative translational, rotational and vibrational energy. Increasing either the vibrational or rotational energy decreases the association cross sections. Quasiclassical trajectories, which initiate (CH 3) 2O with zero-point vibrational energy, give thermal rate constants which approximately 50% smaller than those for trajectories initiated with no vibrational energy. The trajectory rate constants for Li + (CH 3) 2O association are smaller than those calculated from canonical variational transition state theory. This difference results in part from a dynamical recrossing of the transition state in the trajectories. A bottleneck appears to be present for intramolecular vibrational energy transfer from Li + + (CH 3) 2O relative translation to (CH 3) 2O internal rotation and vibration degrees of freedom. A comparison of trajectory, transition state theory and adiabatic capture theory methods for calculating association rate constants is given.