ADIABATIC APPROXIMATION AND NONADIABATIC EFFECTS FOR OPEN-SHELL ATOMSIN AN INERT SOLVENT - F-ATOMS IN SOLID KR

The dynamics of P-state F atoms in solid Kr is studied by molecular dy namics simulations in two frameworks: (i) The adiabatic approximation, in which nuclear motion is confined to the lowest adiabatic potential surface of the system; (ii) A method that treats semiclassically non- adiabatic transitions between electronic states in the course of the d ynamics. The simulations deal with the spectroscopy of the F atom at d ifferent lattice sites, and with orbital reorientation dynamics due to the coupling with lattice vibrations. Also explored is migration of t he F atom, following the preparation of an exciplex Kr2+F- which disso ciates radiatively in the lattice. Some of the main findings are: (1) p-orbital reorientation dynamics on very short timescales (t less than or similar to 20 fs) is dominated by non-adiabatic mechanisms. Adiaba tically, reorientation effects have timescales of the order of 0.25 ps or longer. (2) Lattice vibrations of particular symmetry types are pa rticularly efficient in inducing p-orbital reorientation. (D) Dissocia tion of a Kr2+F- exciplex can result in migration of the F atom into s everal lattice sites. The F atom spectroscopy for the different sites is different, and can be experimentally distinguished. (4) The migrati on probabilities of the F atom calculated adiabatically are much great er than the non-adiabatic ones. The results shed light on the coupling between electron orbital and nuclear dynamics for P-state atoms in so lids.