Structural anomalies in solid deuterohydrogen

X-ray studies of pure deuterohydrogen (containing less than 0.4% isotopic impurities) are carried out in the temperature range 4.5–16.5 K. The obtained low-temperature value of the HD hcp lattice volume is V0 = 21.58 cm3/mole. It is was found for the first time that the ratio c/a of the lattice parameters at low temperatures is 1% lower than the ideal value. Such a comparatively large deviation is unusual for solid hydrogens. The observed effect is explained by the presence of “admixtures” of higher rotational states induced by additional stronger (as compared to those in homonuclear isotopes) anisotropic forces associated with the asymmetry of HD molecule. The sign and order of magnitude of the theoretical estimates for ξ=c/a−8/3 are in accord with the experimental data.

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