States of Helium Atoms Adsorbed on Krypton and Xenon Crystals

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Abstract
The quantum‐mechanical state of a He atom absorbed on the (100) face of Kr and Xe crystals has been studied. The variational function for the adsorbed atom has been constructed using a linear combination of the Bloch sums of local functions corresponding to suitable three‐dimensional anharmonic oscillators. The probability distribution for the coordinates of the He atom has been described by a set of isodensity curves similar to those normally employed when studying atomic or molecular orbitals. The gap between the energy bands corresponding to the fundamental and first excited state implies that, at the lowest experimental temperatures, the surface mobility must be interpreted in terms of the fundamental state. For the fundamental state, the total energy is higher than the potential barrier to surface migration in the case of Kr and slightly lower in the case of Xe.