Evidence for Ionic Bonding inYH3−δ

The infrared transmission spectra of ${\mathrm{YH}}_{3-\delta }$ and ${\mathrm{YD}}_{3-\delta }$ thin films have been measured in the energy range from 300 to $6000{\mathrm{cm}}^{-1\mathrm{}}$, and the optical constants have been calculated by Kramers-Kronig analysis. From a fit of the frequency-dependent conductivity and the dielectric loss functions with one Drude term and five Lorentz oscillators, the longitudinal and transverse optical-phonon frequencies have been determined. The Born and Szigeti effective charges have been calculated and the ionicities of the ions in ${\mathrm{YH}}_{3-\delta }$ have been derived. We find that hydrogen does not enter as a proton in the compound, but that it is negatively charged, with a Szigeti effective charge of nearly $0.5e$.