Combining transition-state theory with quasiclassical trajectory calculations. Part 5.—Canonical calculations on the reaction: F + H2(v= 0)→ HF(v′)+ H

Abstract

The dynamics of the reaction, F + H₂(v=0)→ HF(v′)+H, occurring at 300 and 1000 K have been examined by the combined TST (transition-state theory)–QCT (quasiclassical trajectory) method which has been developed in earlier papers. In the TST–QCT method, the transition state is determined by finding pods (periodic orbiting dividing surfaces) on fixed-angle potential-energy surfaces for which the action over one cycle of the pods motion is (v+½)h. The complete transition state is defined by joining these pods together, and its phase space is sampled to select starting points for quasiclassical tranjectories, ‘forwards’ towards products and ‘backwards’ towards reagents. The results are compared with those from standard QCT calculations on the same modified LEPS surface (known as Muckerman 5), using of TST to estimate absolute rate constants from our results. Our calculations demonstrate that motion from separated F + H₂(v= 0) to the transition state is highly vibrationally adiabatic and the calculated product vibrational energy distribution is in excellent agreement with that derived from standard QCT calculations. The advantages and limitations of the combined TST–QCT method as applied to canonical bimolecular reactions of species in defined vibrational states are discussed.