Valence-Excited States of Carbon Monoxide

Abstract

Precise quantum mechanical calculations have been performed on the 72 states of carbon monoxide which dissociate to a 3P, 1D, 1S, or 5S carbon atom plus a 3P, 1D, or 1S oxygen atom. A minimal basis set of Slater-type orbitals (optimized for the C and O atoms) was used, and holding the atomic 1s orbitals doubly occupied, full configuration interaction calculations were carried out for all molecular states at no fewer than nine internuclear separations. Seventeen bound states (De ≥ 0.27 eV) were obtained, eight of which have been observed experimentally. The theoretical ordering of known bound states agrees with experiment except for the a 3Π and A 1Π states. This fact is rationalized by noting that these two states have much smaller re values than do the other excited states. The most interesting of the unobserved predicted bound states are the 5Σ+ and 5Π states, which dissociate to 3PC+3PO, and the third 1Π state, with a relatively large calculated dissociation energy. A dominant molecular orbital configuration is associated with each of the first eleven bound states. Calculated spectroscopic constants are compared with available experimental data. Potential curves are presented and discussed for both bound and repulsive molecular states. The A 1Π state has a calculated maximum of 1135 cm−1, in good agreement with the experimentally based estimate (950 ± 150 cm−1) of Simmons, Bass, and Tilford. Calculations were also carried out on the X 1Σ+, a 3Π, and a′ 3Σ+ states using 1s atomic Hartree–Fock orbitals and 2s and 2p STO's optimized for the X state at the experimental re. These calculations correctly placed the a 3Π state below the a′ 3Σ+ and resulted in improved De and re values for all three states.