Analysis of the two-photon D ¹Δ- X¹Σ⁺ transition in CO: Perturbations in the (10-0) band

Spin-orbit perturbations among the D ¹Δ(v = 10), d ³Δ(v= 14), a³Π(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.