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