LATTICE DISTORTION OF AR AND XE CRYSTALS CAUSED BY A HYDROGENIC POINT-DEFECT

Several accurately measured rare gas-hydrogen pair potentials have been used to calculate the host lattice relaxation pattern produced by hydrogen atom impurities at substitutional and octahedral interstitial sites in rare gas crystals. For the interstitial site a large outward relaxation of the first shell was found depending on the choice of potentials. The displacements range from 10% to 16% of the unrelaxed distances in H/Ar and from 6% to 10% in H/Xe. The distortions, though much smaller for the higher order shells, extend to large distances. The formation of the distorted configuration goes along with drastic changes of various physical properties. We give values for the frequency of the localized impurity mode, the defect formation energy and the potential barrier of the cage. Particularly attention is payed to the trapping-site assignment of the H atom with the help of ESR and optical spectroscopy.