Hydrogen, vibrational potential metals

The hydrogen vibrational spectra provide direct information on the strength of the metal-hydrogen interaction and therefore on the hydrogen potential. Accurate knowledge of the hydrogen potential is of fundamental importance for the understanding of many properties of metal-hydro-gen systems, e.g., thermodynamic behavior (chemical potential), diffu-... 

The second term (E - 3 C/2) is the ground state energy of hydrogen dissolved in a metal with respect to atomic hydrogen at rest. E is the vibrational potential minimum measured with respect to atomic hydrogen and 3 C/2 is the zero point energy. 

Figures 17 Surface reflectivity of Pd(111) and Pd(IOO) with and without adsorbed H. The reflectivity is on log scale. The addition of hydrogen shifts and intensifies the lowest energy surface resonance on Pd(111) (5.5 eV). The sharp drop in reflectivity at 8 eV corresponds to the emergence of a surface diffraction beam, and opens a new channel for electron interaction with the surface. The image potential states are just below this emergence threshold. On Pd(IOO) the curves are similar, but the energy scale is reduced due to the different crystal structure of the surface and different-sized surface Brillouin Zone. Reprinted from Surface Science, 178, M.E. Kordesch, Surface resonances in vibrational spectroscopy of hydrogen on transition metal surfaces Pd(IOO) and Pd(111), 578-588, 1986, with permission from Elsevier Science.

A review is presented of some recent applications of neutron vibrational spectroscopy to the study of disordered metal-hydrogen systems. The examples discussed cover a range of systems from simple dilute solutions in bcc or fee metals to amorphous alloy hydrides. It is shown that neutron inelastic scattering studies of the vibrational density of states provide a powerful and sensitive probe of the local potentials and bonding sites of hydrogen in metals and often reveal critical information on the novel microscopic physical properties and behavior of disordered metals-hydrogen systems, including those influenced by interstitial or substitutional defects. 

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