Zero-THz absorption profiles in glassy solutions. High frequency ? process and its characterisation

Abstract

It is established that in addition to the well-documented α and β losses in viscous fluids, there exists a third (γ) process at THz frequencies (far infrared, or submillimetre) which is necessary for the overall time-correlation function of the dipole moment to be well-behaved at short times. The β and γ peaks of the zero-THz loss profile survive in the glassy state as remnants of the microwave and Poley absorptions observable in the liquid at ambient temperature. In order to probe the glassy environment in non-dipolar solvents such as decalin, the behaviour of the following solutes is monitored: dichloromethane (10 % v/v); dibromomethane (3 % v/v); tetrahydrofuran (10 % v/v); toluene (20 % v/v); chloroform (10 % v/v); fluoro-, chloro-, and bromo-benzene (10 % v/v). Some of these solutes are used as probes also into the weakly dipolar glassy environment of o-terphenyl and (10 % pyridine + 90 % toluene). The zero-THz absorption profiles of the solutes display a variety of behaviour above and below the glass transition temperature. For example, CH2Cl2+ decalin has a very pronounced β process in the viscous liquid which is absent from CH2Br2+ decalin. The β process gradually disappears across the halogenobenzene + decalin series from fluoro- to bromo-.