Theory of quantum diffusion in solid hydrogen. II. Fluctuation approach

The kinetics of clusterization of orthoexcitations in solid parahydrogen is studied based on the previously proposed fluctuation mechanism, in which the migrating particle is exposed to a time-dependent field generated by surrounding scatterers with internal degrees of freedom. The different types of interaction of orthoimpurities with ortho-singles and pairs are analyzed and evaluated. It is shown that, along with direct electrical quadrupole interaction, there also exists an indirect interaction, which is of approximately the same intensity and due to the quadrupole dilatation of the lattice surrounding a pair cluster. The expression obtained for the probability of a hop is analyzed for different limiting cases. Estimates of the relaxation times, following from the proposed theory, agree well with the estimates observed experimentally. At low temperatures and for low concentrations, the clusterization time is an increasing function of the temperature. Analysis of the theoretical answers suggest that the clusterization kinetics is more likely to be determined by almost free diffusion of singles (or pairs) rather than by the last hop prior to pair formation.

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