Magnetocatalytic effect on rare earth oxides

Abstract

The rates of ortho–para hydrogen conversion on some self-supported rare earth oxides have been measured at room temperature. The change of the rates by application of a weak external magnetic field has been determined. Only on Pr2O3 and Yb2O3 a small decrease of the rates could be observed. On the basis of two coupled proton spins under the influence of a magnetic field—composed of an extrinsic and an intrinsic part—a simple theory is given which explains the occurrence, the sign and also the field dependence of the magnetocatalytic effect. It is found that the sign depends upon the mutual orientation of the H2 molecules and the magnetic moments of the active sites. Finally, the theory allows us to deduce the well-known formula for the ortho–para hydrogen conversion rate given by Wigner.