Combining transition-state theory with quasiclassical trajectory calculations. Part 6.—Microcanonical calculations on the reaction: F + H2(v= 0)→ HF(v′)+ H

Abstract

Procedures are described for applying the combined TST (transition-state theory)–QCT (quasiclassical trajectory) method to reactions occurring at constant collision energy rather than at constant temperature, as in earlier papers, and results for the reaction F+H₂(v= 0)→ HF(v′)+H are reported. In the TST–QCT method, the transition state is defined by joining together pods (periodic orbiting dividing surfaces) on fixed-angle potential-energy surfaces for which the action over one cycle of the pods motion is (v+1/2)h. The phase space of the transition state is then sampled by appropriate pseudorandom techniques to provide starting points for pairs of quasiclassical trajectories, ‘forward’ towards products and ‘backward’ towards reagents. In applying the TST–QCT method to microcanonical systems, the energies associated with reaction coordinate, bending and overall rotational motions in the transition state are selected using correlations between these motions and those in the separated reagents which were previously established from trajectories run back from the transition state. The results of our calculations on F+H₂(v= 0) are compared with those from the extensive, conventional QCT study of Muckerman on the same potential-energy surface (Muckerman 5). As with canonical calculation using the combined TST–QCT method, there is excellent agreement between the two sets of results.