Rate constants for reactions O( 3P) + X 2 → OX + X (X = Br, I) determined by an RRKM-type statistical algorithm employing Monte Carlo simulation

Abstract

Thermal and crossed molecular beam experiments have independently given information on the reactions O( 3P) + Br 2 → OBr + Br and O( 3P) + I 2 → OI + I, which proceed through long-lived reaction complexes. Our previously described statistical RRKM-type simulation algorithm is now modified to calculate detailed and macroscopic rate constants for these reactions. Good agreement is found with the experimental thermal rate constant for O + I 2, while reasonable results are found for O + Br 2 when a potential energy barrier with a height of 4.2 kJ/mol is included in the entrance channel. A somewhat larger energy barrier may be needed to reach good agreement with experiments. Angular momentum restrictions are shown to considerably lower the rate constants for these reactions. It is demonstrated that the detailed reaction model largely influences the energy dependence of the detailed rate constants, and also that extrapolations to other temperatures for thermal rate constants depend strongly on the potential energy model used.