AB-INITIO STUDY ON THE ELECTRONIC-STRUCTURE OF THE 4(2)SIGMA(-STATES OF CO+() AND 5(2)SIGMA(+) EXCITED)

The electronic structure of the 4 (2) Sigma(+) and 5 (2) Sigma(+) exci ted states of CO+ are studied by using state-averaged complete-active- space self-consistent-field/multireference configuration interaction c alculations at and around the equilibrium internuclear distance R(e) = 2.132 au of the CO 1 Sigma(+) ground state. The results reveal that t he 4 (2) Sigma(+) and the 5 (2) Sigma(+) state are located at 16.0 and 18.6 eV above the CO+ (2) Sigma(+) ground state at R(e) = 2.132 au, r espectively. The 5 (2) Sigma(+) state in the internuclear distance reg ion R = 1.930-2.132 au and the 4 (2) Sigma(+) state around R approxima te to 1.850 au are identified as the lowest Rydberg-type (2) Sigma(+) state. This state has a predominant Rydberg-type configuration 4 sigma (2)6 sigma 1 pi(4) which is composed of a C2+-O ion core (4 sigma(2)1 pi(4)) plus one electron in an s-type Rydberg orbital (6 sigma).