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Intermolecular forces in globular molecules V: transport collision integrals
No full textCollision integrals are tabulated for the spherical shell potential over a range of reduced temperatures from 0.2 to 10.0, for a range of core sizes from 1.20 to 4.0 The results are compared with those obtained for other bireciprocal potential models and the Kihara core model. Potential parameters are deduced from gas viscosity data and compared with those obtained from second virial data alone. The viscosities agree for most models over a rather wide temperature range; however, the thermal-diffusion factors show marked differences especially at low and at high temperatures
Pressure dependence of the diffusion thermoeffect in gases (Dufour effect)
No full textA modified Loschmidt apparatus for the measurement of the diffusion thermoeffect as a function of pressure is described. Measurements are reported for H2-Ar, H2-CO2, and H2-CH 4 for pressures between 1 and 20 atm at room temperature. The experimental results have been explained semiquantitatively in terms of the pressure dependence of the relevant transport coefficients and their first composition derivatives. Terms arising because of the nonideality of the gases are also included in the phenomenological description. Relative values of diffusion coefficients for the three systems determined from the measurements are in good agreement with those determined by other methods, and the effect of pressure on the diffusion thermoeffect parallels the pressure dependence of the thermal diffusion factor as determined from gas-unmixing measurements. Suggestions are made for the future use of the method in determining other transport coefficients
Determination of molecular quadrupole moments from viscosities and second virial coefficients
No full textGas viscosity data for nine quadrupolar molecules are analyzed using calculated collision integrals for the 12-6-5 potential. The parameters of the spherical component of the potential are obtained from the viscosity data, and then used in conjunction with second virial coefficient data to determine the quadrupole moments and 'shape' parameters of the molecules. The quadrupole moments obtained are very reasonable, and further improvement along these lines will probably depend on a better understanding of the non-spherical components of the repulsive part of the potential
Instabilities in ternary diffusion
No full textTwo series of experiments on gaseous diffusion instabilities are reported. In one series the convection cells are made visible with ammonium chloride smoke; the observed behavior appears quite complex. In the other series the stability limits in osmotic diffusion are investigated as a function of pressure and composition for H2-CH4-CO2. Reasonable agreement is obtained with a stability theory based on Rayleigh's treatment of thermal convection
Intermolecular forces in globular molecules III: a comparison of the spherical shell and Kihara models
No full textA series expansion for the second virial coefficient of the spherical shell potential is used to show that this model, in contrast to the Kihara model, does not inadvertently include terms which can represent contributions due to multipolar interactions
Intermolecular forces in globular molecules II: multipolar gases with a spherical-shell central potential
No full textThe integrals appropriate to the classical second virial coefficient for a molecule obeying a spherical-shell central potential and including either a dipole moment or a quadrupole moment are calculated for a wide range of values of r0*, T*. The functions Hk(r0*, T*) are available for k=6, 10, 12, 15, 18, 20, and 24. The results are used to investigate the intermolecular forces in methyl chloride and benzene. In both cases a significant improvement in fit with experimental data is noted upon inclusion of multipolar forces. For benzene, treated as an axial molecule, a quadrupole moment Θ zz of ±15×10–26 esu is deduced