Investigations of the optical spectroscopy of atomic sodium isolated in solid argon and krypton: experiments and...

The absorption spectra of thin film samples, formed by the codeposition of sodium vapor with the rare gases have long been known to consist of complex structures in the region of the atomic sodium "yellow-doublet" lines. The photophysical characteristics of the associated luminescence (excitation/emission) spectra, indicate strong interaction between the excited P state Na atom and the rare gases (Ar, Kr, and Xe) used as host solids. This system is reinvestigated with new experimental spectroscopic results and molecular dynamics (MD) calculations. The so-called "violet" site in Ar and Kr has been produced by laser excitation of thermally deposited samples. The simulation of the "spray-on" deposition of thin films enables identification of tetravacancy (tv) sites of isolation for ground-state atomic sodium in Ar while in Kr this site is found in addition to single vacancy (sv) occupancy. Various cubic symmetry sites were taken into account to simulate absorption and emission spectra using accurate interaction potentials for the Na.RG diatomics. The well-known 3-fold splitting in absorption, attributed to the Jahn-Teller effect, was very well reproduced but the simulated spectra for all the sites considered are located in the low energy region of the experimental bands. The evolution of the excited state Na atom is followed revealing the nature and symmetry of the sites that are transiently occupied. Consistent with the large Stokes shift observed experimentally, there is an extensive rearrangement of the lattice in the excited state with respect to the ground state. Combining all the experimental and theoretical information, an assignment of experimental violet, blue, and red absorption features is established involving single vacancy, tetravacancy, and hexavacancy sites, respectively, in Ar and Kr.