Effect of electronic transition dynamics on iodine atom recombination in liquids

The Langevin stochastic trajectory model used by Hynes, Kapral, and Torrie [J. Chem. Phys. 72, 177 (1980)] to describe secondary recombination of iodine atoms in solution has been generalized to allow for electronically inelastic transitions between the ten I–I potential curves that dissociate to ground state iodine atoms. The electronic transitions are treated via the Miller–George version of the Tully–Preston surface hopping model. The main qualitative result is that electronically inelastic processes substantially slow down the rate (and ultimate probability) of recombination. It is also seen that the electronic inelasticity changes from being strong at large r, where an essentially Boltzmann distribution over the various electronic states is maintained, to being weak at small r, where the distribution is far from Boltzmann.