Dynamics of liquid ammonia from cold neutron scattering

Abstract

The scattering of 4.1 Å neutrons by liquid ammonia has been measured at 218 K in the angular range of 30-90° using the Trombay rotating crystal spectrometer. The experimental data, after correcting for multiple scattering, have been compared with model calculations, and it is shown that it is possible to get detailed information about the rotational correlation function on the basis of neutron experiments alone. The model assumes Langevin diffusion for translational motions. Rotational motions are described by means of an orientational correlation function which has a gaseous behaviour for times up to τ₀ and then changes over to a diffusive character with a rotational diffusion constant D_r. Within the framework of the model the correlation function can be described with D_r=0.28×10¹³sec^-1 and τ ₀=0.57×10^-18sec. Corrections for multiple scattering and their dependence on model parameters are discussed.