ALBERT

Description: [1]  We report measurements of the ultraviolet absorption cross-sections of 32 SO 2 , 33 SO 2 , 34 SO 2 and 36 SO 2 recorded from 250 to 320 nm at 293 K with a resolution of 8 cm −1 . This is the first reported measurement of the 36 SO 2 cross-section. This work improves earlier measurements of the 32 SO 2 , 33 SO 2 and 34 SO 2 cross-sections and is in good agreement concerning fine structure and peak widths, with localized differences at the peak maxima when isotope effects are taken into account. SO 2 samples were produced in an identical process via combustion of isotopically enriched S 0 , eliminating effects due to variation in oxygen isotopic composition. Peak positions for the rare isotopologues are red shifted relative to the 32 SO 2 isotopologue. Starting at the origin the shift increases linearly through the band. A linear shift model based on the spectrum of 32 SO 2 was used to estimate the cross-sections of 33,34,36 SO 2 ; the average of the wavelength resolved absolute difference between the modeled and experimental spectra is 77.4, 107 and 139 ‰ respectively. While the peak-to-valley amplitude of 36 SO 2 tends to be smaller than the other isotopologues throughout the spectrum, integrated band intensities for all isotopologues are conserved to within 4% relative to 32 SO 2 . The cross-sections were used in a photochemical model to obtain fractionation constants to compare with photochemical chamber experiments. We conclude that planetary atmospheres will exhibit isotopic fractionation from both photoexcitation and photodissociation, and that experiments in the literature have isotopic imprints arising from both the B 1 B 1 -X 1 A 1 and the C 1 B 1 -X 1 A 1 bands.