Photophysics of atomic magnesium isolated in solid methane and perdeuteromethane. I. Optical absorption of an impurity species in a quantum solid

Abstract

Optical absorption spectra recorded at 12 K for the 1 P–1 S transition of atomic magnesium isolated in solid methane and perdeuteromethane exhibit significant differences in their spectral positions and bandwidths. The greater blue shift in CD4 relative to CH4 was found to be unchanged upon sample annealing. Shifts in the spectral position of the resonance transition in the two solids are discussed in the context of mass related differences in the lattice parameters of these light solids which is a manifestation of their behavior as quantum solids. From the blue shift observed in CD4 , the isotope having the smaller cage size, it is proposed that repulsive forces dominate in the interaction of the atomic magnesium guest species with its host. The greater bandwidth of the absorption profile in CH4 , relative to CD4 is discussed in terms of a Jahn–Teller model where the effective frequency of the phonon modes coupling with the electronic transition of the optically active impurity are higher in the former solid.