Raman spectroscopy of aqueous methanol solutions under pressure

Abstract

Recently, Dixit et al. (2002) used neutron diffraction to probe the molecular-scale structure of a concentrated methanol–water mixture (7:3 molar ratio) under ambient conditions. Their results suggest that the anomalous thermodynamics of water–alcohol systems arises from incomplete mixing at the molecular level, i.e. most of the water molecules exist as small hydrogen-bonded strings and clusters in a fluid of close-packed methyl groups. The application of high hydrostatic pressure together with Raman spectroscopy is a powerful technique to detect such structural changes in associated systems. In this work, we present measurements of Raman spectra of water–methanol mixtures under pressure at room temperature. We have used an anvil cell device with sapphire anvils to generate pressures up to 10 kbar. Our results allow us to suggest important changes on the cluster distribution as a function of pressure.