Theoretical studies on spectroscopy and atomic dynamics in rare gas solids

Abstract

Challenges of chemical dynamics have been encountered in the present study consisting of five publications, where a theoretical approach has been chosen to clarify the observations gathered by magnetic and optical spectroscopies in solid rare gases. Detailed understanding of the events at a microscopic level is necessitated for control over the basic processes occurring in the solids. The knowledge of atom trapping sites and dynamics gained here is of both practical and academic importance in this research field of chemical physics. In this thesis a combined quantum chemical - classical mechanics approach is adopted. First, accurate ab initio electronic structure methods are used for the atom pairs present in the system in order to parametrize the interaction energies and spectroscopic quantities. Second, the pairwise information is used in molecular dynamics simulations, which yields the time-averaged effects of the surrounding medium on the dopant atom. The electron paramagnetic resonance spectra of H, Li, Na, and B atoms in rare gas solids are simulated by a novel combination of computational tools, and the results agree well with the experiments. Definite assignments for trapping in various lattice geometries with distinct symmetries and volumes have been achieved, and the developed methodology seems promising for future use in studies of more complex cases. Atomic dynamics plays a crucial role in the optical studies, and the present simulations have been successful in associating the experimental observations and the temperature dependent atomic motion to specific trapping configurations of matrix isolated B and S atoms. In particular, both thermal and photoinduced recombinant emissions of S2 have been interpreted with the aid of simulations, and the B atom optical transitions perturbed in the solids have been assigned on the basis of the knowledge of computed otential energy curves, simulated energetics, and combinatory magnetic effects.