Anharmonic force field of ethylene

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Abstract
A simple anharmonic force field of ethylene is proposed. It includes the principal cubic and quartic stretching constants derived from appropriate Morse functions for individual bonds and two other higher‐order constants. The quadratic part consists of general valence type constants that show the characteristics of the Pulay‐Meyer Set II force field. The perturbation method including a general treatment of the first‐ and the second‐order resonances has been used, and about 190 vibrational frequencies of ethylene and six deuterated ethylenes have been calculated to agree fairly well with the experimental values. The proposed potential gives also reasonable values of the Coriolis coupling constants, the centrifugal distortion constants, and the 13C‐isotope shifts. The signs of the compliance constants are consistent with the assumption of monotone changes of internal coordinates on the dehydrogenation into acetylene and on the dissociation into two methylene radicals.

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