Abstract :
Far infrared absorption spectra are reported for a variety of binary mixtures, consisting of liquids with linear, planar and spherical molecular shape. A systematic comparison of the absolute intensities shows that particularly a category of systems containing partners of linear and of planar molecular shape, display ‘effective excess’ absorption intensities. The interaction induced ‘excess’ intensities are interpreted as a sensitive indicator of the formation of liquid ‘transient clusters’ and of the fluctuation of the symmetry in the local environment. It is found, that with increasing molecular anisotropy of the partners, the effect of the ‘excess’ intensities increases and therefore stronger local ordering in the mixture is considered. The origin of the ‘transient clusters’, with a lifetime of tenths of picoseconds, is attributed to quadrupole-quadrupole electrostatic interactions, whereas the packing effects seem to play a predominant role in the short time interaction range (i.e. at higher frequencies of the FIR profiles).
