Estimation of Lennard-Jones Potential Energy Parameters from Liquid Densities.

Abstract

below that of many of the liquids of interest. It was this circumstance which necessitated the alteration of the range of the refractometer described in the preceding paragraph. Even with this range extension it was necessary to use formamide as a secondary reference for measuring the refractive index of carbon tetrachloride, dichloracetic acid and hydrazine.Bayen's dispersion data for water at 17.7°was corrected to 25°u sing his temperature dependence of refractive index. These values were then used as standards for measuring the dispersion of formic acid and the 8 molar urea solution. In order to obtain the refractive index of the sodium bromide solutions at 25°the refractometer was first calibrated at 18°u sing water vs. sodium bromide. The sample temperature was then raised to 25°and the calibration (which is independent of temperature) used to determine the difference in refractive index of water and sodium bromide solutions.Solvents. The solvents used were of the best grade obtainable commercially and were not purified further except for the dioxane and ethylene dichloride which were distilled. The urea was recrystallized once from ethanol. Refractive indices were measured at 25°at the sodium D line with an Abbe refractometer and were: formic acid 1.3692, 8 molar urea

A Correlation of Molecular Parameters for Transport Properties of Polar Gases

“…Dispersion attraction constants for polar gases: O, from dilute gas theory and experimental viscosity; broken line, Mavroyannis-Stephen theory, Equation 5; full line, empirical fit, Equation 6some simple, easily accessible properties. In fact, for the Lennard-Jones 12-6 potential, there have been several methods of estimating the parameters; e.g., from critical constants (Hirschfelder, et al, 1954), from polarizabilities (Brandt, 1956), from the saturated liquid densities at low pressure (Reed and McKinley, 1964), and from critical constants and acentric factor (Tee, et ah, 1966). In this paper the angleaveraged potential parameters are correlated with critical temperatures and polarizabilities.…”

Correspondence Principle for Transport Properties of Dense Fluids. Nonpolar Polyatomic Fluids

“…The cause of the deviation of polyatomic fluids from the simple correspondence principle therefore appears to be either a failure of the molecules to obey the same twoparameter potential function or a density dependence of the intramolecular degrees of freedom (assumptions 3 and 1 of Tham and Gubbins, 1969). Two-parameter potential func-1 Present address, Shell Development Co., Houston, Tex. tions, such as the Lennard-Jones 6,12, do not accurately account for the properties of polyatomic fluids (Reed and McKinley, 1964). The failure of this assumption may be corrected to some extent by introducing a third parameter.…”