Specific heat of solid para-hydrogen

We have developed a vacuum adiabatic calorimeter for studies of cryocrystals and their mixtures over the temperature range 0.4–300 K. We report the specific heat of hydrogen with an ortho concentration of 5 · 10−3 % over the temperature range 0.5–8 K. The limiting value of the Debye temperature obtained as T →0 is found to be Θ0 = 118.5 ±0.5 K. It is shown that the specific heat of solid para-hydrogen, the same as that of other cryocrystals with central-force interactions and close-packed lattices (4He, Ne, Ar, Kr, and Xe), is described at low temperatures by the universal curve Cv = AT3[1 + α1(T/Θ0)2 + α2(T/Θ0)4 + ...] proposed by Barron and Morrison. The influence of sample history on the experimental values of the specific heat of hydrogen is studied with an ortho concentration of x = 0.21 at.% and the time for configurational equilibration in this mixture is estimated.

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