Quantum force molecular dynamics study of the reaction of O atoms with HOCO.

The reaction of HOCO with O atoms has been studied using a direct ab initio dynamics approach based on the scaling all correlation UCCD/D95(d,p) method. Ab initio calculations point to two possible reaction mechanisms for the O+HOCO-->OH+CO2 reaction. They are a direct hydrogen abstraction and an oxygen addition reaction through a short-lived HOC(O)O intermediate. The dynamics results show that only the addition mechanism is important under the conditions considered here. The lifetime of the HOC(O)O complex is predicted to be 172+/-15 fs. This is typical of a direct and fast radical-radical reaction. At room temperature, the calculated thermal rate coefficient is 1.44 x 10(-11) cm(3) mol(-1) s(-1) and its temperature dependence is rather weak. The two kinds of reactive trajectories are illustrated in detail.