When radicals collide with molecules, the open electronic shell character of the radicals may lead to a passage through a multitude of electronic states of the reaction complex and the Born-Oppenheimer approximation of the potential will break down. The contribution of this effect to the rate constant so far has been taken into account only for very few examples. It is difficult to calculate, but it is of large relevance for all radical reactions under astrochemical conditions. This talk reports on recent theoretical results (refs1and 2) for the reactions of HO radicals with C and N atoms. Tentative conclusions on the reaction of HO with O atoms are also discussed.

1. A.I. Maergoiz, E.E. Nikitin and J. Troe, Electronic nonadiabatic effects in low temperature radical-radical reactions I. C + OH, J. Chem. Phys. 141, 044302 (2014)

2. A.I. Maergoiz, E.E. Nikitin and J. Troe, Electronic nonadiabatic effects in low temperature radical-radical reactions II. N + OH, in preparation (2015)