Anisotropic hyperfine interactions of rare-gas nuclei near trapped hydrogen atomsa)

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Abstract
The EPR spectra of hydrogen atoms trapped in xenon and krypton at 10 K have been reinvestigated. Analysis of the anisotropic 129Xe (enriched), and 83Kr hyperfine structure shows the H atoms are trapped in the octahedrally symmetric interstitial site (6 nearest neighbors) of the Kr and Xe matrices. For H in Kr, a simple model which considers only overlap of H and Kr orbitals in purely covalent Kr⋅⋅⋅H ’’molecules’’ accounts very well for the observed Kr hyperfine structure and the electronic g factor. To account for the corresponding magnetic constants of H in Xe, however, it is necessary to consider, along with overlap effects, the effects of transfer of electronic charge from the nearest neighbor Xe atoms to the interstitially trapped H atom, as described by admixture of a very small Xe+⋅⋅⋅H− ionic component into the covalent Xe⋅⋅⋅H ’’molecule’’. This charge transfer may also be a factor in the surprisingly large differences in the g factors and 129Xe hyperfine constants of H and D atoms trapped in Xe.