A model for trap-controlled diffusion was proposed in which diffusing atoms could be captured either by trapping at an empty trap or by exchange with chemically identical trapped atoms of differing isotope number. The equations which described tracer diffusion experiments were solved, and the predictions of the effects of dominant exchange or of dominant trapping were compared. A comparison with data on amorphous hydrogenated material showed that exchange was the predominant capture mechanism in D tracer diffusion measurements. This explained the relatively short distance (some 20nm) which D travelled before trapping. It also reconciled the smoothness of the D tracer diffusion profile, after long times, with the existence of deeply bound (by more than 2.0eV) H in amorphous hydrogenated material.

M.Kemp, H.M.Branz: Physical Review B, 1995, 52[19], 13946-54