Calculation of Force Constants of Ethylene by a Semiempirical ASMO–SCF Method

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Abstract
A semiempirial ASMO–SCF calculation involving all valence electrons was carried out for a number of nuclear configurations of ethylene molecule. From the variation of the ground‐state energy on the change of various structure parameters, all the diagonal quadratic force constants in the internal symmetry coordinate system were calculated and compared with those obtained from vibrational spectra. A modification of the Dewar and Klopman's formula including two empirical parameters was used to represent the core repulsion energy. It gave reasonable potential energy curves for the stretching coordinates.