On the Factors Determining the Molecular Arrangement in Crystalline Ethylene

The orientation-dependent potential energy of the ethylene crystal was calculated using a somewhat modified expression for the dispersion energy in the case of non-axially symmetric molecules. It was concluded that the main force which determines the angle between the bc plane and the C=C bond axis in the ethylene crystal is the dispersion; on the other hand, it is the quadrupole-quadrupole interaction which determines the angle between the ab plane and the C=C bond axis. The expected molecular arrangement in the crystalline ethylene belongs to the space group P21/n, this is consistent with the conclusion obtained from the spectroscopic data.