Analysis of the two-photon D 1Δ--X 1Σ+ transition in CO: Perturbations in the (10--0) band

Spin-orbit perturbations among the D 1Δ(v=10), d 3Δ(v=14), a 3Π(v=18), and a' 3Σ+(v=19) levels of carbon monoxide have been observed in the two-photon laser excitation spectrum of the D 1Δ--X 1Σ+ (10--0) band. Spectra have been analyzed using a weighted nonlinear least-squares-fitting method. Detailed assignments and wave numbers are presented for the D--X (10--0), a--X (18--0), and d--X (14--0) bands. Molecular constants and perturbation parameters have been determined, and mixing coefficients have been calculated. Electronic perturbation parameters associated with the D 1Δ∼a 3Π spin-orbit interaction and the d 3Δ∼D 1Δ isoconfigurational interaction are obtained for the first time. The latter parameter could be determined because of an unusual multiple crossing among the a, d, and D states. The v=18 level is the highest vibrational level of the a 3Π state ever observed