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$O_{2}$ SCHUMANN-RUNGE BAND ABSORPTION OF A STRUCTURED SOLAR SPECTRUM

Please use this identifier to cite or link to this item: http://hdl.handle.net/1811/12979

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Title: $O_{2}$ SCHUMANN-RUNGE BAND ABSORPTION OF A STRUCTURED SOLAR SPECTRUM
Creators: Huestis, D. L.; Slanger, T. G.
Issue Date: 1994
Abstract: $O_{2}$ absorbs solar radiation at wavelength shorter than 242 nm, leading to photodissociation and formation of ozone. In the wavelength range 174-205 nm the $O_{2}$ absorption spectrum consists of relatively sharp peaks, corresponding to transitions to predissociated rovibrational levels of the $B^{3} \Sigma^{-}_{u}$ [the Schumann-Runge (SR) Bands], and relatively deep valleys. Typical widths of the peaks are on the order of $1 cm^{-1}$ (0.004 nm), while the valleys may be $5-40 cm^{-1}$ wide. The complexity and rapid variation of the $O_{2}$ absorption spectrum has prompted a number of studies to determine the absorption cross section and to model the resulting atmospheric absorption. Except near 122 nm, atmospheric modelers largely have assumed that the solar spectrum is relatively smooth and representable by averages over $500 cm^{-1}$ intervals. In fact, the solar spectrum is strongly structured, In the 174-205 nm range only relatively low resolution (0.007 nm or worse) spectra are available, and thus the ``true” intensities of strong features and the underlying background relatively are uncertain. Modulations of $\pm 50%$ are typical in 0.02 nm. A particularly striking case is provided by three $S_{i}^{+}$ lines at 180.80, 181.69, and 181.75 nm, that have intensities at least 20-30 times the mean (perhaps even more, due to limited spectral resolution). The two lines near 181.7 nm overlap three of the rotational lines near the head of the $O_{2}$ 10-0 SR band. We have modeled atomspheric absorption in the Schumann-Runge bands using the best available solar data. We find that the 10-0 band is more important than anticipated in ozone production and that the ozone is produced at higher altitudes. Overall, the altitude dependence of ozone formation is surprisingly insensitive to the fine details of the solar spectrum, at least at the available resolution.
URI: http://hdl.handle.net/1811/12979
Other Identifiers: 1994-FA-02
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