PREDISSOCIATION OF THE B(3)SIGMA(-)(U) STATE OF S-2

Predissociation of the B (3) Sigma(u)(-) state of S-2 has been investi gated by a combination of cavity ring-down spectroscopy and model calc ulations. The experimental spectra of the B (3) Sigma(u)(-) - X (3) Si gma(g)(-) (upsilon', 0) bands for 10 less than or equal to upsilon' le ss than or equal to 22 span the wavenumber range 35480-39860 cm(-1). E xtensive variation is observed in the degree of rotational structure w ithin the vibrational bands because of lifetime broadening caused by p redissociation. Fits to the band contours give homogeneous linewidths for transitions to the B-state vibrational levels for 10 less than or equal to upsilon' less than or equal to 17 that vary from less than or equal to 1 cm(-1) for the (10, 0) band to 7 +/- 1 cm(-1) for the (17, 0) band with a maximum Linewidth of 14 +/- cm(-1) for the (13, 0) ban d. For upsilon' greater than or equal to 18, all bands are completely diffuse, indicating linewidths in excess of 15 cm(-1). The experimenta l results are compared with the results of a theoretical model that us es a Rydberg-Klein-Rees (RKR) potential for the B (3) Sigma(u)(-) stat e, ab initio calculations of the repulsive potentials that cross the B state, and Fermi golden rule calculations of the predissociation rate s for the different repulsive potentials. Minor adjustments to the nb initio potentials, and an estimate of the spin-orbit coupling between the bound and repulsive states enable us to calculate predissociation rates in excellent agreement with the experimental observations. We de duce that the predissociation for upsilon' less than or equal to 16 is predominantly via a (IIu)-I-1 state, whereas for upsilon' greater tha n or equal to 17, coupling to a second repulsive state,suggested to be either a (5) Sigma(u)(-) or (IIu)-I-5 state, provides the primary mec hanism for predissociation. (C) 1998 American Institute of Physics.