Lattice Dynamics of Solid Deuterium by Inelastic Neutron Scattering

The dispersion relations for phonons in solid ortho-deuterium have been measured at 5 °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 ${\mathrm{cm}}^{-1\mathrm{}}$. The elastic constants are deduced and the isothermal compressibility is calculated to be $B^{-1\mathrm{}}=2.19\mathrm{}\times {10}^{-10\mathrm{}}$ ${\mathrm{cm}}^2$ ${\mathrm{dyn}}^{-1\mathrm{}}$. The density of states and the heat capacity is calculated and the Debye temperature is found to be ${\theta }_0=114\mathrm{}$ °K.