A 2PPI, 3DPI VALENCE BOND WAVE FUNCTION FOR 1B1U STATE OF ETHYLENE

A 2 pπ, 3 dπ valence bond wave function for the lowest 1B1 u state of the π-system of ethylene is variationally optimized with respect to the atomic orbital exponents using a non-empirical π-approximation. The resulting energy compares favourably with previous calculations and leads to a satisfactory value for the lowest 1A1g-1B1 u transition energy. The optimized exponent for the 2pπ orbital is close to the Slater value whereas the exponent for the 3 dπ orbital is found to be nearly hydrogenic. The implications of this result are discussed in some detail. © 1969 Springer-Verlag.