THEORETICAL STUDIES OF LIQUIDS

MUSTAFA RASHID IBRAHIM, Purdue University

Abstract

The NVT and/or NPT ensembles were used in the Monte Carlo (MC) simulations of liquid ammonia, dimethyl ether (DME), methyl ethyl ether (MEE), diethyl ether (DEE), and methanol. The computed thermodynamic and structural data such as heat of vaporization, heat capacities, density (NPT), isothermal compressibility, coefficient of thermal expansion, and radial distribution functions are discussed and thoroughly analyzed. Other distributions which have been discussed are the bonding energy distributions and the energy pair distributions. In the case of ammonia and methanol, the distributions of the hydrogen bond number and the hydrogen bond angle are analyzed and discussed. Comparison of the computed results with the available experimental data is made. Generally, the agreement is good. Except for ammonia, the intermolecular interactions were described by Coulomb and Lennard-Jones functions in the TIPS (transferable intermolecular potential functions) format. In the case of ammonia, the intermolecular potential function (12-6-3-1) was derived from ab initio calculations. All the above potential functions assume the pairwise additivity of the intermolecular interactions and neglect higher order contributions. With the aid of ab initio calculations on ammonia trimers, the importance of the three-body effect in liquid ammonia has been analyzed. The internal rotational degrees of freedom for MEE and DEE monomers were included in the simulations. The necessary intramolecular rotational potential functions were obtained from ab initio calculations. Interesting findings are that the conformational equilibria for MEE and DEE monomers are not affected by condensation and that hydrogen bonding in liquid methanol is unaffected by applying high pressure up to 15000 atmospheres. To aid in the construction of intermolecular potential functions for solvent-ion pairs, ab initio calculations have been performed for complexes of hydroxide and methoxide anions with water and methanol. These calculations show that the methanol is a stronger acid and the difference in gas phase acidities of water and methanol is halved by the introduction of one solvent molecule.

Degree

Ph.D.

Subject Area

Organic chemistry

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