Collision time of a triatomic chemical reaction A + BC

Abstract

The collision time is an important quantity of an elementary chemical reaction and describes the speed of the collision process in a collision reaction. In this study, we present a generalized method to calculate the collision time of a triatomic reaction in which the collision time is defined by the sum of the incoming time, the intermediate complex time, and the outgoing time. Two variables including the total distance Rtotal and Ravg, the average value of Rtotal over time, are used to compute the three components of the collision time. We compute three triatomic reactions including Ca + HCl → CaCl + H, O + HCl → OH + Cl/OCl + H, and O + HF → OH + F at different collision energies and initial diatomic vibrational levels using the quasi-classical trajectory method to confirm that the method could be reliable and reasonable. The time evolutions of Rtotal could efficiently classify the direct and indirect reactive mechanisms and reveal a distinct discrepancy of the two mechanisms. As the collision energy and initial diatomic vibrational level increase, the percentage of direct reaction trajectories increases. At the same time, the average and maximal values of collision time decrease. Comparing the maximal collision time and the reactive probability distributions of the products, it could be found that most reactive trajectories’ collision time is less than 2 ps. Moreover, the present calculations indicate that the method could be applicable to estimate the lifetime of the intermediate complex for the reaction systems with deep potential wells and the collision time of the reactions with a direct abstraction mechanism.