Density of states in solid deuterium: Inelastic neutron scattering study

Abstract

The dynamics of solid deuterium (sD2) is studied by means of inelastic scattering (coherent and incoherent) of thermal and cold neutrons at different temperatures and para-ortho ratios. In this paper, the results for the generalized density of states (GDOS) are presented and discussed. The measurements were performed at the thermal neutron time-of-flight (TOF) instrument IN4 at ILL Grenoble and at the cold neutron TOF instrument TOFTOF at FRM II Garching. The GDOS comprises besides the hcp phonon excitations of the sD2 the rotational transitions J=0_s13_s178614_s191 and J=1_s13_s178614_s192. The intensities of these rotational excitations depend strongly on the ortho-D2 molecule concentration co in sD2. Above E=10_s13_s178194_s19meV there are still strong excitations, which very likely may originate from higher-energy damped optical phonons and multiphonon contributions. A method for separating the one-phonon and multiphonon contributions to the density of states will be presented and discussed.