ChemInform Abstract: QUANTUM AND STATISTICAL MECHANICAL STUDIES OF LIQUIDS. 20. PRESSURE DEPENDENCE OF HYDROGEN BONDING IN LIQUID METHANOL

Abstract

The effects of pressure on the structure, thermodynamic properties, and hydrogen bonding in liquid methanol have been studied via statistical mechanics simulations at 1, 5000, and 15,000 atm. The intermolecular interactions were described by the previously reported transferable intermolecular potential functions (TIPS) which include Lennard-Jones and Coulomb terms. The thermodynamic results are found to be in good agreement with experiment; particularly, the density is within 4 to 6% of experimental data across the entire pressure range. Although the range corresponds to a compression of 30%, the hydrogen bonding is essentially unaffected. This is in accord with the pressure dependence of IR and Raman spectra of liquid alcohols. The decrease in volume occurs primarily between the hydrogen-bonded chains with the chains themselves remaining unaltered. The observation is reflected in the interesting behavior of the radial distribution functions (rdfs). The first peaks in the rdfs that characterize the hydrogen bonding (g/sub OO/, g/sub OH/, and g/sub HH/) are suppressed by increasing pressure, while the peaks in the rdfs involving the methyl groups are enhanced. Stereo plots and numerous distributions for the energetics and hydrogen bonding provide a thorough description of the liquid's structure at the molecular level.