Direct dynamics study on mechanism and kinetics of the biradical self-reaction of HOO

A theoretical study of the mechanism and the kinetics for the hydrogen abstraction reaction of the biradical hydroperoxy radical has been presented at the CCSD(T)/6-311++G(3d,2p)//CCSD/6-31+G(d,p) level of theory. Our theoretical calculations suppose a stepwise mechanism involving the formation of a postreactant complex in the triplet and singlet entrance channels. Four transition states of the six-membered chain complexes (3TS1 and 1TS1) and six-membered ring complexes (3TS2 and 1TS2) are located at the high dual level CCSD(T)/6-311++G(3d,2p)//CCSD/6-31+G(d,p) method. The rate constants of Path 1 ∼ Path 4 at the CCSD(T)/6-311++G(3d,2p)//CCSD/6-31+G (d,p) level are calculated by means of the conventional transition state theory (TST) and canonical variational TST without and with small-curvature tunneling (SCT) correction within the temperature range of 200–2,500 K. The calculated results show that the triplet channel is the dominating reaction channel and Path 2 is found to be the most favorable pathway. The rate constants of Path 2 are in good agreement with the experimental values at the experimentally measured temperatures. Moreover, the variational effect is not obvious in the low temperature range but is not neglectable in the high temperature range. The SCT plays an important role particularly in the low temperature range. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011