Quantum diffusion in solid H2: a short review

Abstract

A review is presented on the experimental observations and the theoretical progress made in investigating the quantum diffusion in solid H2. The mechanisms of resonant ortho–para conversion and of quantum tunneling are discussed. It is pointed out that the ortho-H2 clustering reaction process, by which quantum diffusion is detected, needs to be better understood to account for the dependence of the observed reaction-time constant τ on temperature and on ortho-H2 concentration. The general trends in the experimental results are reviewed, and the discrepancies between various determinations of τ are discussed. Further experiments are suggested as well as computer simulations for the clustering procedure. A review is also given on the status of quantum diffusion of HD in solid H2. Recent observations on recombination rates of H and on depolarization rates of muons in H2 that show evidence of quantum effects are briefly mentioned.