Thermally activated processes in Li doped Ar matrices studied by electronic spin-lattice relaxation

Abstract

Optical absorption and ESR spectra were taken simultaneously of Li doped Ar matrices. The measurements showed that the broad absorption near the free atom D1, D2 transitions is in reality a superposition of two spectra, the so-called blue and red triplet, well known from other alkali rare gas systems. Both triplets could be correlated with corresponding ESR spectra. Longitudinal and transversal electronic relaxation times T1 and T2 were determined by carefully analyzing the saturation of the ESR signal amplitudes and the line broadening. The temperature dependence of T1 and T2 suggests that the relaxation is caused by thermally activated local structural changes with an extremely low activation enthalpy of the order of 1 meV. Similar results were obtained in K, Ag, and Au doped Ar matrices.