There are very few works on atomic-hydrogen diffusion on catalysts by QENS, the H species resulting from H2 dissociation have been predominantly studied by INS. When hydrogen is bonded to metal atoms, the heavy atoms can be considered as fixed during the local modes of hydrogen. A consequence is that the mean-square amplitudes for the hydrogen atoms will be generally small so that the sample tem­perature will be of small influence on the INS intensities. Another consequence is that the nondegenerate modes of hydrogen will have nearly the same intensity and an E mode will be twice as intense as an A mode. The INS spectra can thus be fitted and the relative intensities of the bands yield the populations of the various sites.

INS studies of the adsorption of H2 on various materials, to observe rotational transitions, and of various hydrogen species present on metal and sulfide catalysts were previously reviewed [4, 5]. Only recent work will be considered here.