Electronic Structure of Ionized Molecules. VII. Ethylene

Abstract

The potential‐energy surfaces of the neutral C₂H₄ molecule and its positive ion have been studied, and parts of them have been calculated point by point by a semiempirical self‐consistent method (SCF CNDO/2 with slight modifications). The calculations show that (1) the equilibrium configuration of the C₂H₄⁺ ion is twisted ($D_2$ symmetry group). The potential function corresponding to the twisting motion has a double minimum and is remarkably flat. The vibrational structure observed in the different Rydberg states of C₂H₄ and C₂D₄ can be fitted to such a potential function. Values for the angle of twist and the potential barriers have been proposed. (2) The exchange phenomenon occurring among hydrogen atoms (scrambling) in the ion takes place through the asymetrical configuration CH₃CH⁺.