Dipolar behaviour of molecular fluids up to the critical point

Abstract

Far infra-red spectra of chloroform, chlorobenzene and fluorobenzene are reported for the whole range of the liquid state along the orthobaric curve and in the coexisting dense gas. The spectra, and also those of OCS previously published, are interpreted in terms of the correlation function for the rotational velocities . Internal field corrections have been included and an estimate of the contribution due to non-permanent dipole absorption has been subtracted. In the lower density phases (including the liquid a few tens of degrees below the critical point) the rotational motion is a collision-perturbed free rotation. In the dense (cold) liquids the rotational motion at short times is better described as damped librational.