High-Resolution UV Absorption Cross-section Measurements of 32S, 33S, 34S, and 36S Sulfur Dioxide for the B ̵̃^1 B_1-X ̵̃^1 A_1 Absorption Band

High-resolution and high-precision spectrum data presents a challenging measurement. We report newly measured ultraviolet absorption cross-sections of 32SO2, 33SO2, 34SO2, and 36SO2 for the - band over the wavelength range 240 to 320 nm at a resolution of 0.4 cm−1. The resolution is improved by 20 times compared to a previous study (Danielache et al., 2012). A least absolute deviation linear regression method was applied to calculate the cross-sections and spectral errors from a set of measurements recorded at a wide range of pressure to ensure optimal signal-to-noise ratio at all wavelengths. Based on this analysis, error bars on the measured cross-sections ranged between 3 and 10%. The overall features of measured cross-sections, such as peak positions of isotopologues, are consistent with previous studies. We provide improved spectral data for studying sulfur mass-independent fraction (S-MIF) signatures in SO2 photoexcitation. Our spectral measurements predict that SO2 photoexcitation produces 33E = −0.8±0.2‰ and 36E = −4.0±0.4‰, whose magnitudes are smaller than those reported by Danielache et al. (2012).