Figure 31.

The energies of the optically-allowed 1B_u⁺ and the optically-forbidden 2A_g⁻, 1B_u⁻ and 3A_g⁻ states (for vertical transition from the ground 1A_g⁻ state) that have been obtained by ab initio calculations including the σ- and π-electrons by the use of Møller-Plesset perturbation theory with complete active-space configurational interaction (CASCI-MRMP). Approximate linear relations, as functions of 1/(2n + 1), are presented for comparison with Figure 1 (Reproduced from Ref. [32]).