Nonadiabatic molecular dynamics simulation of ultrafast pump-probe experiments on I2 in solid rare gases

Recent experimental studies of both $A$ and $B$ state photoexcitation of ${\mathrm{I}}_2$ and the ensuing many-body dynamics in rare gas matrices by Apkarian and co-workers are simulated using the methods we presented in an earlier work combining nonadiabatic molecular dynamics with semiempirical diatomics-in-molecules (DIM) excited state electronic structure techniques. We extend our DIM methods to compute the ion pair states of the ${\mathrm{I}}_2$ -rare gas crystal system and use these states together with a model of the configurational dependence of the electronic dipole operator matrix elements to calculate the time resolved probe absorption signals in these pump - probe experiments using a simple golden rule result. Our computed signals are in remarkable agreement with experiments and we use our calculations to provide a detailed microscopic analysis of the channels to predissociation and recombination underlying these experiments.