Measurements of high-, room-, and low-temperature photoabsorption cross sections of SO2 in the 2080- to 2950-angstrom region, with application to Io

Using synchrotron radiation as a continuum light source, we have measured t he absolute absorption cross sections of SO2 from 2080 to 2950 Angstrom wit h a resolution bandwidth (FWHM) of 0.5 Angstrom and under temperature condi tions of 400, 295, and 200 K. Significant temperature effects are clearly o bservable throughout the studied wavelength region. Many hot bands have bee n observed, including some in the 2080- to 2220-Angstrom region, where no s uch transitions were previously known. It was also found that the apparent continuum cross section underlying the vibrational features increases by an order of magnitude when the gaseous SO2 temperature increases from 200 to 400 K. The new laboratory cross section data should be useful in constraini ng both the temperature and abundance differences between the leading and t he trailing sides of the Io's atmosphere. (C) 2000 Academic Press.