Search for the origin of synergistic solvation in methanol/chloroform mixture using optical Kerr effect spectroscopy

Abstract

The synergistic effect of methanol/chloroform mixture on solute solvation was earlier attributed to the formation of an extended hydrogen-bonding network in the mixture. Such a network was proposed to be weak through the solute dipole-moment dependent experiment. In this study, we search for signatures of such interactions using the femtosecond time-resolved optical Kerr effect spectroscopy, which is sensitive to the ultrafast intermolecular dynamics. We observed a 2-3-fold retardation of the orientational diffusion time of chloroform molecules that is attributed to the formation of hydrogen-bonds with methanol. Our frequency domain analysis in terms of the excess reduced spectral density and partial reduced spectral density allowed us to detect a hydrogen-bond stretching band around 90 cm−1 (with 107 cm−1 natural frequency) associated with methanol molecules simultaneously accepting a hydrogen-bond from chloroform and donating a hydrogen-bond to another methanol molecule. Additionally, in an auxiliary mixture used in this study, where chloroform is replaced with carbon tetrachloride, we found evidence of carbon tetrachloride-methanol halogen-bond formation; however, its signature in the spectra is much weaker than in the case of chloroform-methanol hydrogen-bonding.