THEORETICAL CALCULATIONS OF ZERO-TEMPERATURE ABSORPTION-SPECTRA OF LIIN SOLID H-2

We employ variational and diffusion Monte Carlo methods to calculate. the ground state properties of both pure and Li doped solid Hz. The ab sorption spectra of Li in the H-2 solid are calculated from the sample d ground state configurations and a pseudothermal semiclassical spectr al line theory, based on the Franck-Condon principle for a condensed p hase system. The T=O numerical results of various thermodynamic proper ties of the pure and doped solid agree well with those from. previous theoretical calculations. However, the Li spectra differ significantly from results of a finite temperature path integral Monte Carlo calcul ation [D. Scharf et al., J. Chem. Phys. 99, 9013 (1993)], which employ ed a different Li-H-2 potential. The differences in two calculations are extensively discussed here, and comparisons are also made with ava ilable experimental data. We demonstrate that accurate measurements of the Li absorption spectrum provide a powerful means to probe the loca l structures of the Li trapping sites. (C) 1996 American Institute of Physics.