Density functional studies on HO+BrO and HO2+Br reactions

Abstract

The potential energy profile (PES) of the [HBrO₂] system has been studied at density functional theory level using the 6-311G(2df,2pd) basis set. The structural parameters of the isomers of [HBrO₂] have also been optimised at second-order Moller–Plesset perturbation (MP2) and complete active space (CAS(12,12)) self-consistent field levels using respectively, the 6-311G(2df,2pd) and 6-31G** basis sets. Three isomers, of relative thermodynamic stability HOOBr (1)>HOBrO (2)>HBrO₂ (3), have been identified and characterised as energy minima. Besides these covalently bound minima, various loose hydrogen-bonded complexes [OOH···Br 5a(s), 5′a(t) and O···HOBr 7a(t)] have been located on the singlet and triplet PES. Isomerisation, molecular elimination and direct hydrogen abstraction saddle points have been traced and a qualitative understanding of the mechanism and kinetics of the stratospherically important HO+BrO, HO₂ +Br reactions has been derived.