Low frequency molecular modes in liquid hydrocarbons

Abstract

The spectral distribution of slow neutrons scattered at low angles by straight chain hydrocarbon liquids has been measured. For pentane, measurements were made at six different points in PVT space, and the data analyzed by comparison with various models. Properties studied include the diffusion coefficient, the activation energy for diffusion, the time for a diffusive step, the size of a proton's thermal cloud and the spectral density for low frequency (∼10¹² Hz) modes of motion. The diffusion data agree well with those obtained by other techniques but the magnitude of the diffusive step time is not well determined for these liquids. A pronounced peak in the low frequency region of the spectral density function has been discovered, and may be associated with short time local bonding between molecules.