Carbon dioxide molecular diameter

The pair correlation function is a short range quantity in liquids, decaying to unity after a few molecular diameters, the correlation length However, in supercritical fluids g(r) has a much longer range and t, becomes considerably larger than the mean inter-molecular separation at the critical density. For instance, for carbon dioxide , = 5.5 nm at Tc compared to the mean intermolecular separation of 0.55 nm (Eckert, Knutson and Debenedetti 1996). 

Gas-viscosity measurements yield molecular diameters of 2.58 A (angstroms) for helium, 3.42 A for argon, and 4.00 A for carbon dioxide. With these values, calculate and c/i3 from Eq. (V-36), and calculate D i and Z i3 using Eq. (V-34). Compare with your experimental values. 

The basic molecular characteristics of these species are reflected by the potential parameters given in Table I. Thus, the energy parameter c (proportional to the component critical temperature) increases from carbon dioxide to water, while the parameter a (molecular diameter) is the highest for acetone. 

To confirm the permanent porosity of the sample, a gas sorption isotherm is necessary, which is commonly carried out by nitrogen at 77 K. Argon with smaller size and spherical molecular shape can measure pore surface area and pore volume more precisely. When the pore size is too small to be entered by nitrogen, carbon dioxide and hydrogen with smaller kinetic diameters can be used instead. The gas sorption behavior is determined by the adsorbate, the temperature and pressure, and the structural characteristics of adsorbent such as pore size and shape, surface area, and pore volume. By virtue of the diversified and unique structures, MOFs have demonstrated many interesting properties potentially useful for practical applications. 

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