lambda and gamma reversal: The dissociation-limit region of the B-3 Sigma(-)(u) state of O-2

Using narrow-bandwidth vacuum-ultraviolet radiation generated by difference -frequency four-wave mixing in Xe, the O-2 photoabsorption cross section in the Schumann-Runge system B (3)Sigma (-)(u)<--X (3)Sigma (-)(g), near the dissociation limit of the B state, is measured with a resolution of similar to0.1 cm(-1) full-width at half-maximum. The rotational structure of B-X(2 2,0) is assigned for the first time, and evidence is found for transitions into the F-1 levels of B(v=23). Experimental values for the triplet-splitti ng constants lambda and gamma for B(v=22) are found to be inconsistent with the rising trend observed for v less than or equal to 19, due to a change in the sense of the perturbation of the B-state levels by the C-' (3)Pi (u) levels near B(v=20). A new value for the dissociation energy of the B stat e, D(B)=57 136.2 +/-0.3 cm(-1), determined from an analysis of the observed and missing lines near the dissociation limit, is in excellent agreement w ith previous values arising from the observation of rotational thresholds i n the Schumann-Runge continuum. (C) 2001 American Institute of Physics.