MO Treatment of Acetylene Including All Electrons

The s. p -o. (split- p -orbital) method, II. Further definition and application to acctylene

In part I (Dewar & Hojvat 1961) we described a modification of the l.c.a.o. method designed to allow for the effects of vertical correlation (Dewar & Schmeising 1959, 1960) in unsaturated molecules. We showed that this split- p -orbital (s. p -o.) method gave estimates of the N-V and N-T excitation energies in excellent agreement with experiment, unlike other non-empirical methods. Here an alternative derivation of the s. p -o. method is given to meet certain criticisms that have been raised and the method is then applied to acetylene with very satisfactory results. In this case the agreement with experiment seems better than for any previous treatment, empirical or non-empirical.