Influence of Chain Dynamics on the Far Infrared Spectrum of Liquid Methanol-Water Mixtures.

摘要

Far-infrared absorption spectroscopy has been used to study the low frequency ((center-dot) 100 cm(sup -1)) intermolecular modes of methanol in mixtures with water. With the aid of a first principles molecular dynamics simulation on an equivalent system, a detailed understanding about the origin of the low frequency IR modes has been established. The total dipole spectrum from the simulation suggests that the bands appearing in the experimental spectra at approximately 55 cm(sup -1) and 70 cm(sup -1) in methanol and methanol-rich mixtures arise from both fluctuations and torsional motions occurring within the methanol hydrogen-bonded chains. The influence of these modes on both the solvation dynamics and the relaxation mechanisms in the liquid are discussed within the context of recent experimental and theoretical results that have emerged from studies focusing on the short time dynamics in the methanol hydrogen bond network.