MATRIX-ISOLATION SPECTROSCOPY OF METAL ATOMS GENERATED BY LASER ABLATION .2. THE LI/NE, LI/D2, AND LI/H2 SYSTEMS

Results of experiments on lithium-doped cryogenic solids (Ne, D2, and H2) prepared by laser ablation of solid lithium are presented, including near UV-visible absorption spectra and thermal annealing studies. Li atoms are found in more than one type of trapping site in each of the systems studied. In Li/Ne matrices deposited at T=5 K, the main optical absorption feature is a so-called ''triplet'' absorption with peaks near 628, 641, and 650.5 nm. This observation extends this familiar result from heavier alkali/rare gas matrices to the lightest M/Rg matrix. In Li/D2 and Li/H2 matrices deposited at T=3 K, the main absorptions show an ''asymmetrical doublet'' pattern with peaks near 655 and 672 nm and 650 and 671 nm, respectively. The successful isolation of Li atoms in such light matrix host systems supports previous conjectures about the microscopic mechanism for trapping fast laser ablated atoms. Several highly symmetrical hypothetical Li atom trapping site structures are proposed and discussed in conjunction with the results of the classical Monte Carlo simulations reported in the following article of this journal. The observed absorption line shapes are best explained in the context of a Jahn-Teller effect caused by dynamic distortions of the trapping sites by lattice vibrations, with negligible matrix modification of the Li atom spin-orbit splitting.