Theoretical rate constant calculations for O(³<i>P</i>) with saturated hydrocarbons

Abstract

Abstract Theoretical rate constants have been calculated for O( 3 P ) with five saturated hydrocarbons, CH 4 , C 2 H 6 , C 3 H 8 , iso‐C 4 H 10 , and neo‐C 5 H 12 . The method of choice is bond energy–bond order (BEBO) with activated complex theory (ACT). Because the BEBO method is empirical, O( 3 P ) + CH 4 is evaluated first, and the theoretical results are compared to more rigorous calculations and to the empirical transition state method. Comparisons are also made between predictions and experimental results. All of these comparisons show that the BEBO‐ACT method gives results which are consistent with experiment and other theory. Because the method is successful, the other four cases are then considered. Ambiguity arises for the higher hydrocarbons from the problem of internal rotations in the activated complexes, and three cases are evaluated. Best agreement with experiment is obtained if the primary rotor(s) in the complexes are considered to be free. Predictions of rate constants are made from 500 to 2500 K. Throughout the discussion issues of theory which are common to any ACT calculation from any method of potential energy evaluation (LEP, LEPS, or ab initio quantum mechanics) are featured.