Zero–THz liquid phase absorptions and the rotational Langevin equation

Abstract

Solutions of the Langevin equation for rotational Brownian motion in the needle, sphere, symmetric top and asymmetric top are compared with experimental data over the MHz to THz frequency range. The liquids involved are 2-chloro-2-nitro-propane, the mono-halogenobenzenes, nitrobenzene and benzonitrile. While the microwave data are matched, the theoretical absorptions regain transparency too slowly compared with observations in the far infrared. The powerful mathematical techniques used in solving the Langevin equation should be applied to new types of stochastic equations of motion.