Adiabatic potentials corresponding to 62 electronic states, arising from various configurations of the C2-molecule which consists of two carbon atoms with two 2p-electrons each, are calculated taking into account the effect of 2s-shells. The complete adiabatic Hamiltonian of eight electrons, but not a so-called interaction operator, is used, and direct, exchange, higher permutation, and overlapping integrals are all taken into account. The same effective charge χ is assumed for 2s, 2pσ, and two 2pπ orbitals, and the minimum electronic energy is obtained by varying χ for each nuclear distance. It found that 2s-shells repel 2pσ electrons and attract 2pπ-electrons. Thus (s2 σ2, s2 σ2)1Σg+ state, which was found to be attractive and deepest when the effect of 2s-shells was neglected in the previous paper, becomes very higher and repulsive. The results of the present calculation are that the deepest state is (s2 σπ, s2σπ)1Δg and that (s2σπ, s2σω)1Σg+ and (s2σπ, s2πω)1Πu are next and third respectively.
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Araki et al. (1951) studied this question.