Far infrared spectroscopic studies of the molecular dynamics and interactions of pyridine in organic solvents

Abstract

Abstract Liquid mixtures of pyridine with carbon disulphide, benzene and carbon tetrachloride have been studied in the 2–30 cm −1 region as a function of concentration and temperature. Absorption spectra in this region have been combined with known dielectric data to calculate total dipole moment correlation functions. The data have been fitted to the Gaussian cage model of Steele and Lynden-Bell and variations in spectral and model parameters have been interpreted in terms of the molecular dynamics and interactions. In particular, the role of interaction-induced processes has been assessed in the light of previously known induced excess intensity phenomena, especially for solutions containing carbon disulphide. The behaviour as a function of concentration is largely what is expected for a dipolar molecule in a non-polar solvent, but there are anomolous intensity effects associated with interaction-induced phenomena. Variations with temperature (for x (pyr)=0.8 solutions) are less easily understood and, in particular, display an increasing torque with increasing temperature. This illustrates the potential dangers of fitting multi-process data to a simple librational model. Nevertheless, the spectra do enable us to examine the short and intermediate time regime in these mixtures (0.1–5 ps) and attempt to identify different phenomena occurring on this time scale.