Extending the approach of the temperature-dependent potential to the small alkanes CH4, C2H6, C3H8, n-C4H10, i-C4H10, n-C5H12, C(CH3)4, and chlorine, Cl2

Abstract

Abstract The concept of the temperature dependence of the binary intermolecular interaction potential is extended to anisotropic molecules. The effective Lennard-Jones (n−6) potentials with explicitly temperature-dependent potential parameters e(T) (potential well-depth) and Rm(T) (separation at minimum energy) are successfully applied to the alkanes CnH2n + 2 (n=1–5), and Cl2. The potential parameters e(T), Rm(T) and n (repulsive parameter) are determined by simultaneously fitting thermophysical equilibrium (second pVT and acoustic virial coefficients, B(T) and β(T), respectively) and transport data (viscosity η(T) and self-diffusion coefficients ϱD(T)). For these molecules it is shown that an effective isotropic temperature-dependent potential reproduces the experimental input data for pure gases and their binary mixtures within the range of the stated experimental accuracy. The root-mean-square deviations between experimental and calculated data are by 7%–70% smaller using the Lennard-Jones (n−6) temperature-dependent potential compared to its temperature-independent analogue. Correlations are found for the potential parameters with the volume of the molecules, their dispersion interaction energies and the enlargement of the molecular size on account of vibrational excitation.