A reinvestigation of the c(3)Pi-X-1 Sigma(+) (0-0) absorption band of carbon monoxide

The forbidden c(3)II-X(1)Sigma(+) (0-0) absorption band of carbon monoxide has been reinvestigated under different pressure conditions using the 10.7- m VUV spectrograph at Meudon. Overlap with the allowed (CII)-I-1-X(1)Sigma( +) (0-0) band at lower transition energy has been taken into account. We ha ve identified a new rotational branch corresponding to an S-type branch and extended the analysis to both higher and lower J. An analysis of the band structure and the low J transition lines suggests that the band gains its i ntensity predominantly as a result of an interaction of the c(3)II state wi th a (1)Sigma(+) state, most likely the C(1)Sigma(+) (nu = 0) state. Molecu lar constants have been obtained for the c(3)II state that are in reasonabl e agreement with those previously published. The apparently anomalous small value for the centrifugal distortion constant is explained by a homogeneou s perturbation with the k(3)II valence state. (C) 2000 Academic Press.