A MODEL OF THE B1-SIGMA+-D'1-SIGMA+ RYDBERG-VALENCE PREDISSOCIATING INTERACTION IN THE CO MOLECULE

The strong interaction between the B 3s-sigma (1)SIGMA+ Rydberg state and the D' (1)SIGMA+ valence state of the CO molecule is shown to cause large changes in the vibrational and rotational constants of the B state, as well as predissociation of all rotational levels of B (upsilon' = 2) and a breaking off in the emission of B (upsilon' = 1) levels at J = 36 in C-12 O-16 and J = 37 in C-13 O-16. A two-state diabatic model of the Rydberg-valence interaction is constructed and vibrational term values, widths, and intensities are calculated by close coupling in order to account for the strong mixing. The model separates the differences between the spectroscopic constants of the B state and those of the ground state molecular ion into two components, one due to the R-dependent quantum defect of the B state and another due to the strong Rydberg-valence perturbation. The perturbation is characterized by a constant coupling matrix element of 2900 cm-1 inside the crossing point of the two diabatic potentials, decaying to zero at long internuclear distances. Basically good agreement is found between the model and experiment for shifts in vibrational and rotational terms and for predissociation widths and relative band intensities. The second breaking off in emission in the B (upsilon' = 1) rotational series is used to estimate the height of the long-range barrier maximum in the D' (1)SIGMA+ state to be about 1048 +/- 19 cm-1 above the ground state dissociation limit. Comparison of predicted widths from the two channel close coupled model with those from a single channel adiabatic model shows differences on the order of a factor of 2.