X-ray studies of solid <i>n</i>-H2

The results of precise x-ray studies of normal hydrogen from 2°K to the triple point are reported. Temperature dependences of the lattice parameters, molar volume, linear and volume expansion coefficients of n-H2 have been obtained. An increasing contribution to the thermal expansion of the crystal was found with decreasing temperature which is due to the presence of a rotational subsystem in n-H2. It is shown that near the melting point the thermal expansion of n-H2, similarly to that of p-H2, is essentially anisotropic. The thermodynamic properties of n-H2 are analyzed. The results obtained are evidence of the existence of an isomorphic phase transition in solid n-H2 in the premelting region.

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