Cavity ring-down spectroscopy (CRDS) has been employed to probe the C?1A??X?1A ?(?*??) absorption system of jet-cooled disulfur monoxide (S2O) molecules. Vibronically resolved features possessing up to 8 quanta of excitation in the ?2? S-S stretching mode of the C? state have been characterized, with the onset of rapid predissociation for v2??4 being manifest in the widths of band contours. Measured vibronic intensities are in good accord with predictions derived from a Lie algebraic (or vibron) treatment of Franck-Condon factors for the corresponding S2O emission spectrum. © 2000 Elsevier Science B.V.