Laboratory measurements of photoabsorption cross sections of SO tex2html_wrap_inline12 between 190 and 220 nm.

P.L. Smith (CURSOAR Technologies and CfA), G. Stark (Physics Department, Wellesley College), J.C. Pickering, A.P. Thorne, G. Cox (Imperial College, London)

Determination of the chemical composition of the atmosphere of Io from Hubble Space Telescope observations in the 190-220 nm wavelength region requires knowledge of the photoabsorption cross sections of SO tex2html_wrap_inline12 at temperatures ranging from 110 to 300 K. We have initiated a laboratory program to measure SO tex2html_wrap_inline12 absorption cross sections with very high resolving power ( tex2html_wrap_inline18 ) and at temperatures appropriate to the Io atmosphere. Previous photoabsorption measurements, with tex2html_wrap_inline20 , have been unable to fully resolve the very congested SO tex2html_wrap_inline12 spectrum. Our measurements are being undertaken at Imperial College, London, using an ultraviolet Fourier transform spectrometer (Thorne et al. 1987. J. Phys. E 20, 54). We present new room temperature SO tex2html_wrap_inline12 photoabsorption cross sections in the 190-220 nm region measured with an instrumental resolution of 0.0004 nm. These high-resolution cross sections are compared to previous, lower-resolution, data. This work is supported by NASA Grant NAGW-5200.