Inelastic Neutron Scattering from Pressurized Ethane

Abstract

Motions of the ethane molecule have been investigated at room temperature by inelastic neutron scattering techniques. Ethane targets were observed both in the gas and liquid phases by means of pressure variation. The University of Michigan four‐rotor mechanical monochromator was used to obtain data at scattering angles of 90 and 22 deg for neutron energies in the range 0.046 to 0.020 eV. Triple‐axis‐crystal spectrometer measurements were also made at 0.035 and 0.064 eV as verification. These data indicate that there is no significant difference in the scattering properties of ethane in the gas and liquid state. Effects of the torsional motion of the two methyl groups about the C–C bond can be seen in the forward‐angle data. Comparison of experiment with theory indicates that a Krieger—Nelkin model which includes a harmonic‐oscillator representation of the torsional motion approximately predicts the observed data. The influence of multiple scattering on the final energy distribution has been observed and is discussed.