Theoretical and experimental investigation of the reaction BH+D2→BHD2

Abstract

The rate of the association reaction, BH+D2→BHD2 is determined both theoretically and experimentally. In the theoretical calculations, potential-energy surface information is obtained using multiconfiguration self-consistent-field and large-scale multireference configuration-interaction calculations with large correlation consistent basis sets. The preferred direction of approach is found to be along a non-least-motion pathway for which the BH and DD bonds come in nearly parallel to one another. The small computed activation energy of 2.6 kcal/mol for this highly exothermic reaction is found to arise almost exclusively from changes in zero-point vibrational energy. The experimental measurements of the BH disappearance rate are made at temperatures from 298 to 597 K and are shown to be only weakly dependent on total pressure over the range of 1–100 Torr. As a test of the proposed mechanism, we observe the growth of BD and find the BD appearance rate constant to be in excellent agreement with that for BH disappearance. The measured reaction rates are compared to the results of canonical variational transition-state theory calculations of the association rate and are found to be in excellent agreement.