The intermolecular force constants of highly polar gases

Abstract

The intermolecular force constants of methanol, ethanol, n-propanol, iso-propanol, acetone, water, ammonia, and methyl chloride were determined for six different models of the Leiden second virial coefficient - Stockmayer, polarizable dipole, dipole-quadrupole, steric, Model A, and Model B. The long-range intermolecular forces considered were the dipole-dipole interaction, the dipolei induced dipole interaction, the dipole-quadrupole interaction, and the quadrupole-quadrupole interaction. In addition to these long-range effects, the nonspherical shape of the polar molecule was considered. All models reproduced the experimental Leiden second virial coefficients well except for acetone. The potential constants were reasonable with the proper trend in the linear alcohols. The Stock-mayer force parameters are different from those previously published in the literature. The Stockmayer model should not be considered a complete model although a good fit of the experimental data was obtained. The long-range dipole-induced dipole interaction termsshould be included in a model which describes the Leiden second virial coefficient of highly polar compounds. Also the long-range dipole-quadrupole interaction should possibly be included in the potential function but a more definite conclusion will have to wait until experimental quadrupole moments are available. With the addition of the long-range interaction terms to the Stockmayer potential, the potential parameters change in a direction as to approach more closely the Stockmayer potential parameters from viscosity data. To obtain the same potential parameters from two different sources of data such as Leiden second virial coefficients I and viscosity, the -model should be fitted simultaneously to both experimental data sets.