We simulate the 395 nm photodissociation of I-2(-) embedded in clusters of 6 to 22 CO2 molecules. In the isolated molecule, photodissociation at this wavelength leads exclusively to spin-orbit excited iodine (I*) plus I-. In the larger clusters we observe efficient electronic relaxation, leading both to dissociated products containing ground-state iodine and to recombined products containing I-2(-). The time scale and cluster size dependence of the spin-orbit quenching process agree well with experimental determinations of Sanov et al. (companion paper). The simulation trajectories show that spin-orbit quenching occurs by resonant charge transfer from solvated I- to a nascent I* atom. A model derived from the theory of electron transfer reactions in solution illustrates that this resonance arises when the I spin-orbit energy is compensated by the difference between the solvation energies of the ion and the neutral.