Molecular Multipole Moments Determined from Viscosity and Second Virial Coefficients

Abstract

The quadrupole moment of CO2 molecule and the octopole moment of CH4 molecule have been estimated from the temperature dependence of second virial coefficients. The central potential employed was the Kihara model for which the force constants were derived from the temperature dependence of dilute gas viscosity on the assumption that the multipole moments had no measurable effect on the viscosity. The values of the moments obtained are very reasonable. The shape parameter of the CO2 molecule has been calculated and discussed.

On the determination of the intermolecular potential between a tetrahedral molecule and an atom or a linear or a tetrahedral molecule—application to CH4 molecule

“…The result may be split [3] into an electrostatic contribution (Velec) (coming from the first-order term of the perturbation calculation), an induction contribution (Vi~a) and a digpersion contribution (Vdi~p) (coming from the secondorder terms). This gives qlq2, T (21) …”

“…In fact this table indicates that the most important contribution to B(T)-B(~ is precisely the dispersion one (84 per cent of B(T) -B(~ for T=448.2 K to 88 per cent for T= 176.7 K). So, the second virial coefficient may be considered as a relatively safe tool to get information concerning the hyperpolarizability (in addition to the choice of the Lennard-Jones parameters) but not concerning the octupole moment as already proposed [15][16][17]21]. For instance, if we take only the dispersion term in the computation, we obtain A=2-51 instead of 2.35 x 10-32cm 4 (this calculation was performed with c/k=137 K and o=3.882 A).…”

“…On the other hand, through the equation of state of multipolar gases, the octupole moment of CH 4 has been determined by introducing only the influence of this moment in the angle dependent part V a of the binary potential [15][16][17]21].…”

“…account in V a the contributions Velec (up tO the hexadecapolehexadecapole term), V~la2 and V~2A, leads to the following expression for the mean squared torque per unit density : 'A]2114(y)}(21) +---~-\o 9] I1s(y)+32 \so/ Note that the 1716 coefficient comes from the addition of the octupole-hexadecapole effect (1287/2) and of the hexadecapole-octupole one (2145/2).…”

Thermodynamic Properties of Quadrupolar Mixtures in the Gaseous and Liquid Regions

“…For carbon dioxide-methane, negative deviations resulted between the experimental and calculated values for all the data, and the optimum value of «h for this system was found to be 0.122. Methane is not quadrupolar but does have a substantial octupole moment (Datta and Singh, 1971). It can system should be higher than that calculated from , = 0.074 and less than e2'.…”