FINE-STRUCTURE DEPENDENCE OF PREDISSOCIATION LINEWIDTH IN THE SCHUMANN-RUNGE BANDS OF MOLECULAR-OXYGEN

Fine-structure-specific predissociation Linewidths have been calculate d for the v = 0-18, N = 0-40 levels of the B (3) Sigma(u)(-) state of O-16(2) using a predissociation model which takes into account spin-or bit interactions between the B (3) Sigma(u)(-) state and the 1 (1) Pi( u), 1 (3) Pi(u), 1 (5) Pi(u), and 2 (3) Sigma(u)(+) states, and spin-e lectronic and L-uncoupling interactions between the B (3) Sigma(u)(-) and 1 (3) Pi(u) states. The model parameters were optimized by compari ng the calculated widths with existing measurements of fine-structure Linewidth for v = 0, 14-18, and new determinations for v = 1, 2, 5, 7, 9-13 which have been obtained from existing cross sections for the (v ,0) and (v,1) Schumann-Runge bands using a fitting procedure which ass umes unequal Linewidths for the triplet fine-structure components. The L-uncoupling interaction is found to be important for all vibrational levels in determining the width ratios for the fine-structure compone nts, even at quite low rotational levels. The calculated linewidths va ry from 0.03 (for v = 16, N = 30, F-1) to 4.8 cm(-1) (for v = 4, N = 4 0, F-3), and good agreement is found between the measurements and the model calculations for most vibrational levels. The calculations are e xpected to be useful in the construction of state-of-the-art models de scribing the photochemistry of the middle atmosphere. Greatly improved predissociation model parameters, in good agreement with ab initio ca lculations, have been obtained for the (3) Pi(u) and (1) Pi(u) states, while the (3) Sigma(u)(+) parameters remain the most uncertain. The m odel parameters resulting in the best fit to the widths also give good agreement with observed perturbations in the Schumann-Runge band orig ins. It is found that the actual separations between triplet fine-stru cture levels consistently exceed values predicted from grenerally acce pted spectroscopic constants for the B (3) Sigma(u)(-) state, suggesti ng that a reevaluation of those constants may be in order.