Theory of Quantum Diffusion in Solid Hydrogen and Deuterium. I. Calculation of the Jump Frequency

The jump frequencies of orthohydrogen impurities in solid parahydrogen due to intermolecular interchange and to resonant ortho–para conversion are calculated. The conversion process, due to the nuclear magnetic dipole–dipole interaction and reduced by the tumbling motion of the ortho molecules induced by the quadrupole–quadrupole interaction, is shown to be responsible for the observed quantum diffusion. The interchange process is completely negligible because of the rotational reduction effect. The quantum diffusion in solid deuterium is predicted to be more than two orders of magnitude slower than in hydrogen. The temperature dependence of the jump frequencies is very small.