Neutron scattering and far infra-red spectra of a heavy hindered rotator: CH2Br-CHFBr

Abstract

Neutron scattering spectra have been measured at two temperatures for CH₂Br-CHFBr, a hindered rotator. An analysis giving the density of states spectrum of quantized motions is presented and the effects of non-quantized translational motions in the liquid are described by a jump diffusion model. A correspondence between the density of states spectra and far infra-red results has been found which is striking since the two spectra arise from quite different interactions. In this molecule the neutron scattering comes from the hydrogen motions whilst the infra-red absorption is associated with the electron displacements in the bonds. The connection between these spectra is discussed by introducing correlation functions for the nuclear position and the electric dipole moment changes in the vibrational modes. Qualitatively hydrogen is seen to act as a probe of the molecular dynamics.