Natural Ortho-Para Conversion Rate in Liquid and Gaseous Hydrogen

Abstract

We measured natural ortho-para conversion rates within a wide region of hydrogen fluid states: at temperatures 17-32 K in the liquid and at temperatures 40-120 K in the gas for densities up to 0.09 g/cm3. The experimental data for the gas phase are interpreted within the framework of a theory, the basic distinction of which from Wigner's approach is that we take into account the dependence of the closest distance in a collision of two orthomolecules on their velocity (i.e., temperature). Our theory yields results in good qualitative agreement with experiment in the gas phase. In order to describe the entire bulk of conversion rate data in the hydrogen fluid phases we suggest a convenient interpolation formula, which has reasonable physcial grounds.