Hydrogen vibrations in gamma-TiH and gamma-ZrH under high pressure

The effect of high hydrostatic pressure on the vibrational spectra of monoh ydrides gamma-TiH and gamma-ZrH was studied by inelastic neutron scattering , the maximum experimental pressure being, respectively, P = 15 and 17.5 kb ar. There was observed a uniform linear pressure-induced energy shift of ea ch spectrum compared to that at ambient pressure with proportionality facto rs of 1.02 for gamma-TiH and 1.03 for gamma-ZrH. The observed linear shift of the one-phonon hydrogen modes and the bound multiphonons (biphonons and triphonons) is indicative of a pressure-induced increase of the anharmonici ty parameters in the model Hamiltonian representing the strength of two-pho non and three-phonon interactions.