Inelastic Neutron Scattering Measurements and Ab Initio Calculations of Hydrogen in Single-Crystal Palladium

Using a single-crystal sample of PdH, we have measured the inelastic form factor for exciting the proton from its ground state to various excited states as a function of crystal orientation. Because of the anharmonicity of the potential well which splits otherwise degenerate states, each inelastic form factor could be measured individually. Agreement between theory and experiment is excellent, both with regard to the transition energies and to the modulation of the intensity, giving confidence in the quantum treatment of the proton and hence in the use of the model to predict other properties of the system.