Rotationlike Motion of Molecules in Liquids: Far-Infrared Absorption of Polar Molecules in an Inert Solvent

The far-infrared spectra of a variety of relatively small polar molecules dissolved in a hydrocarbon solvent have been investigated. The absorptions can be attributed primarily to rotationlike motions and the observed bands can be treated in terms of a collision-affected, resonant, rotationlike process. An effective energy-separation parameter ν0 and a collision parameter Δν are deduced for the observed bands, and the values found are consistent with the model used.