X-ray diffraction study and models of liquid ethane at 105 and 181 K

The structure functions for liquid ethane at (1) T = 105 K and a molecular density ρ = 0.012 70 Å−3, and (2) T = 181 K and ρ = 0.011 10 Å−3 have been derived from new x-ray diffraction data. Treating the –CH3 group as a single scattering site, carbon–carbon (methyl–methyl) intermolecular pair distribution functions have been obtained from the structure function data by Fourier inversion. Using Monte Carlo simulation, no two-site exponential-6 interaction model, with sites at the observed C–C bond length, could be found which reproduce the carbon–carbon distribution function. By considering a different class of interactions models, a model was found which reproduced the distribution function derived from experiment and accurately predicts the second virial coefficient of ethane.