Quantum diffusion in solid H2

A study of quantum diffusion in solid H₂ is reported based on the measurement of the pressure versus time at constant volume. Solid samples with ortho-H₂ concentrations between 0.01 and 0.025 were investigated over the temperature range 0.4–4 K. The characteristic time constant for ortho pair formation or breaking up and the resulting pressure changes are presented and compared with other experiments and with theory. The pressure change calculated from a simple statistical model is in good agreement with the experiment and this leads to the conclusion that both in-plane and out-of-plane pairs appear to form (or break up) at the same rate, at least in our concentration range. The experiments also suggest that the concentration dependence of is in qualitative agreement with theory, which, however, makes no predictions on the temperature dependence. Comparison with other experiments also suggests that might be a function of strains in the sample.Supported by a grant from the National Science Foundation.Duke Medical School, Duke University