Theoretical study of the decomposition of BCl3 induced by a H radical.

We report on a theoretical study of the gas-phase decomposition of boron trichloride in the presence of hydrogen radicals using ab initio energetic calculations coupled to TST, RRKM, and VTST-VRC kinetic calculations. In particular, we present an addition-elimination mechanism (BCl(3) + H → BHCl(2) + Cl) allowing for a much more rapid consumption of BCl(3) than the direct abstraction reaction (BCl(3) + H → BCl(2) + HCl) considered up to now. At low temperatures, T ≤ 800 K, our results show that a weakly stabilized complex BHCl(3) is formed with a kinetic law compatible with the consumption rate measured in the former experiments. At higher temperatures, this complex is not stable and then easily eliminates a chlorine atom. Our work also shows that a very similar mechanism, involving the same intermediate and sharing the same transition state, allows for the elimination of HCl. A dividing coefficient between these two elimination pathways is obtained from both a potential energy surface based statistical analysis and an ab initio molecular dynamics transition path sampling simulation. It finally allows partitioning of the global consumption rate of BCl(3) in terms of the formation of (i) BHCl(3), (ii) BHCl(2) + Cl through a H addition/Cl elimination mechanism, (iii) BCl(2) + HCl through a H addition/HCl elimination mechanism, and (iv) BCl(2) + HCl through direct abstraction.