A Spectroscopic Perturbation Origin for Sulfur Mass Independent Fractionation via the B-X System of S2

Abstract

The Great Oxygenation Event (GOE), the introduction of O 2 into the Earth's atmosphere approximately 2.4 billion years ago, is a critical signpost in the development of life on Earth. The vanishing of sulfur isotope anomalies, called Sulfur Mass-Independent Fractionation (S-MIF), in the rock record is thought to be correlated with oxygenation of the early atmosphere. However, the mechanism for the generation of S-MIF in an anoxic atmosphere is unknown. Here, I propose a mechanism that involves spectroscopic perturbations in the B-X UV band system of S 2 . This proposal is based on a global deperturbation analysis done by Green and Western a b and work that I presented previously at this conference in 2015 (MG12) and 2016 (MG08). Specifically, perturbations of the "bright" B state by a "dark" B" state cause some isotopologues to have longer average excited state lifetimes than others. I demonstrate a difference between the shorter-lifetime symmetric (e.g. 32 S-32 S) isotopologues of S2, for which nuclear permutation symmetry causes half of the rotational lines to be missing, and the longer-lifetime asymmetric isotopologues (e.g. 33 S-32 S). I also comment on general features of the B/B" system of S 2 that make it uniquely well-suited to generate a large MIF isotope effect. a M.E. Green, C.M. Western, A deperturbation analysis of the B 3 Σu − (v' = 0-6) and the B" 3 Πu (v' = 2-12) states of S 2 , J. Chem. Phys. 104 (3) (1996) 848-864. b M.E. Green, C.M. Western, Upper vibrational states of the B" 3 Πu state of 32 S 2 , J. Chem. Soc., Faraday Trans. 93 (3) (1997) 365-372.