Density of states in solid deuterium: Inelastic neutron scattering study

TL;DR

This study investigates the vibrational and rotational dynamics of solid deuterium using inelastic neutron scattering, revealing detailed density of states and the influence of molecular composition on excitations.

Contribution

It provides new measurements of the generalized density of states in solid deuterium, including rotational and phonon excitations, and introduces a method to distinguish one- and multi-phonon contributions.

Findings

Density of states includes phonon and rotational excitations.

Rotational excitation intensities depend on ortho-D2 concentration.

High-energy excitations likely from optical phonons and multi-phonon processes.

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 ->1 and J = 1 -> 2. The intensities of these rotational excitations depend strongly on the ortho-D2 molecule concentration co in sD2. Above E = 10 meV there are still strong excitations, which very likely may originate from higher energy damped optical phonons and multi-phonon contributions. A method for separating the one- and multi-phononon contributions to the density of states willbe presented and discussed.