Lattice Dynamics of Solid Deuterium by Inelastic Neutron Scattering

The dispersion relations for phonons in solid ortho-deuterium have been measured at 5 \ifmmode^\circ\else\textdegree\fi{}K by inelastic neutron scattering. The results are in good agreement with recent calculations in which quantum effects are taken into account. The data have been fitted to a third-neighbor general force model. The effective force constants which are obtained show that the bond stretching forces between nearest-neighbor molecules are dominant and this bond stretching constant is 174 dyn ${\mathrm{cm}}^{\ensuremath{-}1}$. The elastic constants are deduced and the isothermal compressibility is calculated to be ${B}^{\ensuremath{-}1}=2.19\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ ${\mathrm{cm}}^{2}$ ${\mathrm{dyn}}^{\ensuremath{-}1}$. The density of states and the heat capacity is calculated and the Debye temperature is found to be ${\ensuremath{\theta}}_{0}=114$ \ifmmode^\circ\else\textdegree\fi{}K.

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