Photogeneration of atomic hydrogen in rare gas matrices

Trapping and thermal migration of the first- and second-row atoms in Ar, Kr and Xe crystals

Trapping and temperature-induced migration (TIM) of the first- and second-row atoms A from H to Ne in the face-centered cubic rare gas RG = Ar, Kr and Xe crystals are investigated within the classical crystal model parameterized by the empirically modified pairwise potentials. New ab initio coupled cluster A-RG potentials computed in a uniform way for all the atoms A are used to represent the atom-crystal interactions. Absolute and relative stabilities of the substitutional and interstitial trapping sites, their structures, interstitial migration pathways, related activation energies and rough estimates of the TIM rates are obtained. The isotropic model, which neglects non-zero atomic electronic orbital momentum, reveals that migration of interstitial atoms along the network of conjugated fcc octahedral voids is the generic case for atomic mobility. Anisotropic interactions with a crystal inherent to P-state atoms B, C, O and F are accounted for using the non-relativistic diatomics-in-molecule method. Depending on its sign, interaction anisotropy can alter the structures of interstitial trapping sites and transition states remarkably. This, in turn, can dramatically affect the TIM rates. Comparison with reliable experimental data available for oxygen and hydrogen indicates a systematic overestimation of the measured activation energies, by 30% at worst. A comprehensive literature review accomplished for other atoms reveals a lack of information on the TIM processes and rates, though makes it possible to verify a part of the present results on the trapping site energies and structures.