In the present Letter, state dependent dissociation rate coefficients in diatomic gases with non-equilibrium vibrational and electronic excitation and chemical reactions are studied. A widely used Treanor-Marrone model is generalized to take into account state-to-state vibrational and electronic distributions. The influence of electronic excitation on the rate of dissociation from various electronic states of CO molecules is estimated. (C) 2004 Published by Elsevier B.V.