High-Resolution\nUV Absorption Cross-Section Measurements\nof <sup>32</sup>S, <sup>33</sup>S, <sup>34</sup>S, and <sup>36</sup>S Sulfur Dioxide for the B1B1−X1A1 Absorption Band

We report newly measured high-resolution and high-precision\nultraviolet\nabsorption cross-sections of <sup>32</sup>SO<sub>2</sub>, <sup>33</sup>SO<sub>2</sub>, <sup>34</sup>SO<sub>2</sub>, and <sup>36</sup>SO<sub>2</sub> for the B̃1B1−X̃1A1 band over the wavelength range of 240 to\n320 nm at a resolution of 0.4 cm<sup>–1</sup>. The resolution\nwas improved 20 times compared to that in a previous study. A least\nabsolute deviation linear regression method was applied to calculate\ncross-sections and derived spectral errors from a set of measurements\nrecorded at a wide range of pressures to ensure the optimal signal-to-noise\nratio at all wavelengths. Based on this analysis, error bars on the\nmeasured cross-sections ranged between 3 and 10%. The overall features\nof measured cross-sections, such as peak positions of the isotopologues,\nare consistent with previous studies. We provide improved spectral\ndata for studying sulfur mass-independent fraction (S-MIF) signatures\nduring SO<sub>2</sub> photoexcitation. Our spectral measurements predict\nthat SO<sub>2</sub> photoexcitation produces S-MIF enrichment factors <sup>33</sup><i>E</i> = – 0.9 ± 0.2‰ and <sup>36</sup><i>E</i> = – 3.8 ± 0.4‰ (where <sup>33</sup><i>E</i> and <sup>36</sup><i>E</i> are\n1000 × [ln(<sup>33</sup><i>J</i>/<sup>32</sup><i>J</i>) – 0.515 ln(<sup>34</sup><i>J</i>/<sup>32</sup><i>J</i>)] ‰ and 1000 × [ln(<sup>36</sup><i>J</i>/<sup>32</sup><i>J</i>) – 1.90\nln(<sup>34</sup><i>J</i>/<sup>32</sup><i>J</i>] ‰, and <sup>3<i>x</i></sup><i>J</i> is\nthe <sup>3<i>x</i></sup>SO<sub>2</sub> photoexcitation rate\nconstant). Based on this new result, we found that calculated SO<sub>2</sub> photoexcitation isotope effects are smaller than previously\nthought and generally do not match photoexcitation experimental observations\nsupporting the hypothesis of an intersystem crossing origin of MIF\non those experiments.