Theoretical Rates and Correlation Functions in Ortho-ParaH2Conversion on Paramagnetic Surfaces

Abstract

A theoretical study of ortho-para hydrogen conversion on paramagnetic surfaces is given. In the absorbed layer, hydrogen molecules are assumed to behave like plane rotators, and their translation at the surface is described by means of a two-dimensional diffusion equation. The spatial dependence of the dipolar matrix elements is found to be important only in the close vicinity of surface impurities. Ortho-para time-correlation functions are computed, and their behavior is compared to the nuclear relaxation case. The total conversion probability is calculated, and two extreme cases are distinguished: (i) The ortho-para conversion energy goes to the thermal bath and the conversion rate is proportional to the diffusion constant and (ii) the ortho-para conversion energy goes to the spin impurity system. In contrast to Leffler's results, the best catalysts are found to be those which have the shortest impurity relaxation times.