Electronic States of C2-Molecule, I: Interacion between p-Electrons

Electronic states of a C2 -molecule are discussed by the method of atomic orbitals without taking into account an effect of inner shells of the component C-atoms. Adiabatic potentials are numerically computed for all states which arise from configurations consisting of two atoms with two p-electrons each. Binding energies and equilibrium distances for attractive states are evaluated from these potentials. It is found that (2 p σ 2 , 2 p σ 2 ) 1 ∑ g + and (2 p σ 2 , 2 p σ2 p π) 3 Π u are the deepest and first excited state respectively, and that (2 p σ2 p π, 2 p σ2 p π) 1 Δ g is a highly excited state in contradiction to the Pauling theory. However the present study is the first step and the result is not conclusive for the C2 -molecule. We shall find in the next paper that the order of the states will be changed when we shall take into account the effect of 2s-shells.