The concentration dependence of the vibrational linewidth and shift in liquid binary mixtures: An analytical model

The concentration dependence of the vibrational line shape of molecules in liquid binary mixtures is explained with an analytical model [E. W. Knapp and S. F. Fischer, J. Chem. Phys. 74, 89 (1981)] which accounts simultaneously for the static and dynamical aspect of concentration fluctuations at the reference molecule. The influence of the diffusion dynamics is small and is responsable for line narrowing with rising temperature. According to this model the concentration dependence may be classified with respect to the total line shift δΩ and the total change of the line width ÄÃof the pure substance versus infinite dilution. The agreement with available experiments is good. The model makes also specific predictions upon the concentration dependence of the frequency shift and asymmetry of the spectral line profile in terms of the interaction with nearest neighbors and their diffusion dynamics.