Hydrides localized vibrational modes

Finally, neutron-scattering experiments on several RH(D)2+x-systems revealed localized vibrational modes ascribed to H vibrations on O and on T sites, wbich are summarized in table 17. A third (higher-energy) peak is sometimes observed in superstoichiometric samples and attributed to the lowered symmetry of a tetrahedral site (T ) in the neighborhood of an x-atom. The role of SRO and LRO in the Ho-sublattice upon the evolution of the local modes (both their concentration- and temperature dependence) in a series of RH(D)2+x hydrides (R=Y, La, Ce, Tb, Dy) was demonstrated recently by... 

Actually, the energies of vibrational states of molecules can be described by both models, where the NM model expresses well low vibrational states and the LM model modes that are localized in a particular group of atoms. In most cases, overtones of hydride stretching vibrations, that is, X—(X = C, N or O) are better described by the LM model due to their relatively small couplings to other bonds. 

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