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Peter L. Smith (Harvard-Smithsonian CfA and CURSOAR), G. Stark (Wellesley College), J. Rufus (Imperial College)
The most prominent EUV emission features in the airglows of Titan and Triton, where N2 is the major atmospheric constituent, originate from the N2 c\prime4~1{\Sigma}\rm u(v=0) level. We report new photoabsorption measurements of 43 rotational line oscillator strengths in the c\prime4(0)-X(0) band of N2. These are the first measurements of individual line f-values for this band. Such values, which are important for models of atmospheres at various temperatures, cannot be reliably calculated from band f-values and Hönl-London factors because of perturbations; the P- and R-branch intensity distribution in absorption deviates systematically from that of an isolated 1\Sigma - 1\Sigma band, as expected from the interactions of the c\prime4(0) level with nearby Rydberg and valence states. In addition, the variation of the band f-value calculated from the sums of pairs of R- and P-branch lines indicates that the c\prime4(0)-X(0) f-value is slightly temperature dependent. A summation over the integrated cross sections of the measured lines yields a room temperature band f-value of 0.132±0.020. \par SO2 is an important constituent of the atmospheres of Io and Venus. Accurate photoabsorption cross section data at the temperatures of these planetary atmospheres are required for the interpretation of SO2 observations and for reliable photochemical models. Our very high-resolution (\lambda/\Delta\lambda \approx 450,000), room-temperature absorption spectra SO2 absorption cross sections in the wavelength region 198 to 220~nm [Stark et al., JGR Planets 104, 16,585 (1999)] are being extended to lower temperatures. Preliminary results and their application to the atmosphere of Io will be discussed. \par This work was supported in part by NASA Grant NAG5-6222. The authors gratefully acknowledge the advice and assistance of K.\ P.\ Huber, A.\ P.\ Thorne, and K.\ Yoshino.
The author(s) of this abstract have provided an email address for comments about the abstract: gstark@wellesley.edu