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

The potential energy profile (PES) of the [HBrO2] system has been studied a t 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 stab ility HOOBr (1)> HOBrO (2)> HBrO2 (3), have been identified and characteris ed as energy minima. Besides these covalently bound minima, various loose h ydrogen-bonded complexes [OOH ... Br 5a(s), 5'a(t) and O ... HOBr 7a(t)] ha ve been located on the singlet and triplet PES. Isomerisation, molecular el imination and direct hydrogen abstraction saddle points have been traced an d a qualitative understanding of the mechanism and kinetics of the stratosp herically important HO+BrO, HO2 +Br reactions has been derived.