THERMALLY-INDUCED ORTHO-PARA CONVERSION ANOMALY IN SOLID HYDROGEN UNDER PRESSURE

The spontaneous ortho-para conversion rate in solid hydrogen under pressure has been observed to increase by approximately an order of magnitude at temperatures greater than 0.08 θo and for molar volumes less than 19.7 cm3. This effect, which disappears upon cooling below these temperatures, cannot be understood in terms of present theoretical models. The heat capacity experiment (CV(V,T)) in which these effects were observed gives an equation of state for parahydrogen for pressures less than 2 kbar which agrees with previous high pressure work at 4.2 K, and a T=0 equilibrium molar volume of 23.20 ± 0.05 cm3. © 1979.