Abstract
The cycloaddition of ethylene is theoretically analyzed for portions of the excited singlet and triplet hypersurfaces using a combination of semi-empirical and intermediate level ab initio techniques. The semi-empirical UHF calculations on the addition of triplet ethylene and methyl radical to ethylene showed that these two reactions have comparable theoretical parameters, including activation energies, spin transfer and spin polarization at the transition state. For the 2S + 2S excited singlet state surfaces, the results of both the ab initio and semi-empirical calculations are qualitatively the same and correspond to the classical ideas generated from orbital symmetry rules. At the ab initio level the results are quantitatively poor, partially due to the use of an intermediate level configuration interaction treatment. In particular, it was not possible to obtain other than a small fraction of the total estimated valence correlation energy in cyclobutane. The configuration interaction problem for both ab initio and semi-empirical calculations is discussed in detail.
Published Version
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