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[16.03] S₂ in planetary atmospheres: a coupled-channel Schrödinger equation calculation of the B ³\Sigma_u^- - X ³\Sigma_g^- transition

S.T. Gibson, S.J. Cavanagh, B.R. Lewis (Australian Nat'l U.), G. Stark (Wellesely College), P.L. Smith (Harvard-Smithsonian CfA)

Diatomic sulfur (S₂) has been observed in absorption, via the strong ultraviolet B ³\Sigma_u^- - X ³\Sigma_g^- system, in the atmospheres of Jupiter and Io. The determinations of S₂ abundances and temperatures from its ultraviolet absorption signature are hindered by the very large uncertainties associated with the fundamental spectroscopic parameters of the molecule. Oscillator strengths, line widths and line shapes are, to date, poorly determined. As part of a combined program of calculations and laboratory measurements, we present preliminary model calculations of the S₂ B - X absorption spectrum. From limited spectroscopic information, it is known that the B ³\Sigma_u^- state is heavily perturbed by B^{\prime\prime 3}\Pi_u, ¹\Pi_u and ⁵\Sigma_u^-(⁵\Pi_u) predissociating states (Wheeler et al. 1998) which yield an apparently complex spectrum. In contrast, the analogous B - X transition in molecular oxygen (O₂), responsible for the Schumann-Runge bands, has been studied extensively in the laboratory. The apparent complexities of this spectrum are readily understood, in terms of a coupled-channel Schrödinger equation (CSE) model (Lewis et al. 2001). We apply a CSE model developed for the B ³\Sigma_u^- - X ³\Sigma_g^- transition of O₂ to the analogous S₂ spectrum, employing the potential energy curves and coupling scheme of Wheeler et al., as a starting point.The CSE calculations provide valuable insight into the photodissociation spectrum, demonstrating complex interference effects that are more pronounced than for O₂ and hence of significance to planetary photochemical models. These calculations will guide planned measurements of the strengths and lineshapes of the B-X system. References: M. D. Wheeler, S. M. Newman, and A. J. Orr-Ewing, J. Chem. Phys. 108, 6594-6605 (1998); B. R. Lewis, S. T. Gibson, F. T. Hawes, and L. W. Torop, Phys. Chem. Earth (C) 26, 519-526 (2001).

The author(s) of this abstract have provided an email address for comments about the abstract: Stephen.Gibson@anu.edu.au

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.