Jump rates of muonium and hydrogen in diamond were calculated by quantum transition-state theory, based on the path-integral centroid formalism. This technique permitted the study of the influence of vibrational mode quantization upon the effective free-energy barriers ΔF for impurity diffusion, which were renormalized with respect to the zero-temperature classical calculation. For the transition from a tetrahedral (T) site to a bond-center (BC) position, ΔF was larger for hydrogen than for muonium, and the opposite happens for the transition BC→T. The calculated effective barriers decrease for rising temperature, except for the muonium transition from T to BC sites. The calculated jump rates were in good agreement with available muon spin rotation data.

Diffusion of Muonium and Hydrogen in Diamond. Herrero, C.P., Ramírez, R.: Physical Review Letters, 2007, 99[20], 205504