MATRIX-ISOLATION SPECTROSCOPY OF METAL ATOMS GENERATED BY LASER ABLATION .1. THE LI/AR, LI/KR, AND LI/XE SYSTEMS

Results of experiments on lithium doped rare gas solids (Ar, Kr, and Xe) prepared by laser ablation of solid lithium are presented, including near UV-visible absorption spectra, and photobleaching and annealing studies of the matrices, as well as visible emission spectra of the laser ablated Li plume. The UV-visible absorption spectra of Li/Ar and Li/Kr matrices generated by cocondensing the rare gas and laser ablated Li atoms at 12 K are dominated by a "blue-shifted triplet" absorption not observed in previously published studies. Control experiments on Li/Ar and Li/Kr matrices generated using a Knudsen oven as the Li atom source showed exclusively an "unshifted triplet" absorption, in agreement with previous studies. The new absorption features are attributed to Li atoms trapped in novel sites in the Ar and Kr solids; sites not accessible to Li atoms generated by the conventional Knudsen effusion technique. Spectra of Li/Xe samples prepared by the laser ablation method showed exclusively the unshifted triplet absorption pattern, in agreement with previous Knudsen effusion studies. All of these observations are explained by a simple model which compares the sizes of the various trapping sites in the rare gas solids to the collision diameters obtained from the Li atom-rare gas atom pair potentials.