The Role of Excited Electronic States in Hypervelocity Collisions: Enhancement of the O(³P) + HCl → OCl + H Reaction Channel

The role of excited electronic states in the O + HCl reaction was studied using the quasi-classical trajectory method for collision energies between 1 and 5.5 eV. Global potential energy surfaces were developed for the ground (³A′′) and first excited (³A′) electronic states of the OHCl system using an interpolating moving least-squares-based method for energies up to 6.5 eV above the reactant valley. High-accuracy ab initio data were computed at automatically selected points using an 18-electronic-state model and the generalized dynamically weighted multireference configuration interaction (GDW-MRCI) method extrapolated to the complete basis set limit. The results show significant dynamical differences between ground- and excited-state reactions. At high collision energies, over half of the total OCl reactive flux originates from reactions on the ³A′ state, whereas OH is produced almost exclusively by the ³A′′ state. Inclusion of the excited electronic state, therefore, dramatically alters the OCl/OH product branching ratio