Ab initio calculations for (BrO) 2 system and quasiclassical dynamics study of BrO self-reaction

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Ab initio quantum mechanical studies for BrOOBr peroxide and its isomers were carried out at the MP2 level of theory using the 6-311+G(2d) basis set. Three minima were determined which are in good consistency with previous density functional theory calculations. On the basis of the ab initio results a simple analytical potential energy surface (PES) was constructed and quasiclassical trajectory calculations (QCT) for the self-reaction of BrO radical were performed. Reactive cross-sections, rate coefficients and branching ratios for the two reactive channels are calculated for a series of initial relative kinetic energies which compare favourably with the experimental trends. The quantum mechanical calculations and the analysis of the trajectory results support the experimental evidence that the reaction proceeds through an energetically enriched conformer of BrOOBr peroxide. In addition, the increasing collision lifetime with decreasing collision energy indicates a possible weak stabilization of a short-lived collision complex at lower temperatures which must be responsible for the increasing importance of the rate coefficient of the secondary channel as the temperature decreases, in consistency with the experimental evidence.