High-Temperature Expansion for the Orientational Specific Heat of Solid H2 and D2

Terms up to order (ΓkBT)5 in the high-temperature expansion of the orientational specific heat of ortho-para alloys of solid H2 or D2 are evaluated. Good agreement is obtained between theory and experiment using a Padé approximant and effective values of the quadrupolar coupling constant, ΓeffΓ0=0.83 for D2 and ΓeffΓ0=0.80 for H2, where Γ0 is the value for a rigid lattice. These values agree with other determinations of Γeff, whereas the T-2 approximation for the specific heat yields anomalously small values of Γeff.