Ortho-para conversion of solid hydrogen as a function of density

The ortho-para conversion in solid H₂ as a function of density has been studied experimentally by isochoric measurements and Raman scattering. We do not find the double peak observed earlier by Pedroni et al., which was attributed to structure in the phonon density of states. Conversion in lattices with nonrandom distributions of ortho molecules is probably responsible for the scatter of the experimental data in the literature. A theoretical model by Berlinsky for conversion involving the one-phonon density of states is used to determine the phonon density of states. This is in good agreement with direct experimental results.