Inelastic neutron scattering studies of defect modes of H in D2O ice Ih

Abstract

The lattice dynamics of ice Ih (H2O, D2O and HDO) have been investigated using inelastic incoherent neutron scattering in the energy transfer range 2-500 meV (i.e. 16-4025 cm-1) using TFXA and HET on ISIS. The spectra of D2O containing different concentrations of H2O from 0.5% to 30% by weight were measured. Three main peaks at approximately 105, approximately 185 and approximately 408 meV associated with three localized modes, mu 1, mu 2 and mu 3, of the H defect centre have been observed in the neutron spectra. Two Gaussian components can be resolved in the mu 1 mode, at 103+or-0.5 meV and 107+or-0.5 meV, indicating the existence of two different force constants for the H bonds. A lattice dynamical calculation for the H defect in a D2O ice Ih host lattice, based on our two H bond force constants model, shows the three modes in very similar positions to those observed in the measured data and, in particular, predicts the splitting of the mu 1 peak into modes at 103 and 107 meV.