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

Ab initio quantum mechanical studies for BrOOBr peroxide and its isomers we re 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 resul ts a simple analytical potential energy surface (PES) was constructed and q uasiclassical trajectory calculations (QCT) for the self-reaction of BrO ra dical were performed. Reactive cross-sections, rate coefficients and branch ing ratios for the two reactive channels are calculated for a series of ini tial relative kinetic energies which compare favourably with the experiment al trends. The quantum mechanical calculations and the analysis of the traj ectory results support the experimental evidence that the reaction proceeds through an energetically enriched conformer of BrOOBr peroxide, Tn additio n, the increasing collision lifetime with decreasing collision energy indic ates a possible weak stabilization of a short-lived collision complex at lo wer 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. (C) 1999 Elsevier Science B.V. All rights reserved.