Sulfur mass-independent fractionation patterns in the broadband UV photolysis of sulfur dioxide: Pressure and third body effects

摘要: Abstract The production of mass-independent fractionation (MIF) in the products middle/far UV photolysis SO 2 isotopologues has been linked to large S-MIF signatures observed pre-2.45 Ga rock record, and provides a valuable proxy for evolution atmospheric O . origin such MIF photolytic recently ascribed optical self-shielding photon-limited regions lower atmosphere. To better characterize signal we have performed pressure-variant broadband experiments –He mixtures. Low pressure (~ 20 Torr) produces extractable sulfur with δ 34 S ≈ 120–180‰, Δ 33 S ~ 20‰, 36 S/Δ S ≈ − 2.5, while near pressures produce S ~ 2‰, S ≈ − 12. Similar conducted variable helium bath gas similar diminution S, both cases S ratio that is linear function over several orders magnitude. We postulate photochemical kinetic these static cell experiments, produced from excited state predissociative dynamics , but cannot expressly rule out as contributor fractionations here.