THEORETICAL-STUDY OF THE EFFECT OF TORSIONAL ANHARMONICITY ON THE THERMODYNAMIC PROPERTIES OF METHANOL

A study is presented of the effect of torsional anharmonicity on the s tructure and thermodynamic properties of methanol. The data are obtain ed from ab initio calculations at the MP2/aug-cc-pTVZ level. It is obs erved that the torsion significantly affects the methyl group. Incorpo rating the experimental data into a one-dimensional model, the barrier to rotation is estimated to be 377.94 cm(-1). Thermodynamic propertie s are calculated using a harmonic model and an anharmonic model where the methyl torsion is considered as a large-amplitude motion. The effe ct of torsional anharmonicity is especially important for the entropy and Gibbs energy as a consequence of the large variation in the molecu lar partition function. (C) 1997 Elsevier Science B.V.