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Photochemistry of Sulfur Dioxide and the Origin of Mass-Independent Isotope Fractionation in Earth's Atmosphere
Annual Review of Earth and Planetary Sciences ( IF 14.9 ) Pub Date : 2017-08-30 , DOI: 10.1146/annurev-earth-060115-012324
Shuhei Ono 1
Affiliation  

Archean sulfide and sulfate minerals commonly exhibit anomalous ratios among four stable sulfur isotopes, 32S, 33S, 34S, and 36S. These anomalous relationships, referred to as sulfur mass-independent fractionation (S-MIF), provide strong evidence for an early anoxic atmosphere. Correlated variations among three isotope ratios (δ33S, δ34S, and δ36S) can be observed in rocks throughout the Archean and are a key clue toward identifying the source reaction of S-MIF. Studies to investigate the origin of Archean S-MIF so far have primarily focused on the photochemistry of sulfur dioxide (SO2). Photolysis of SO2 at wavelengths <220 nm and photoexcitation at 240–340 nm both yield large-magnitude S-MIF. Proposed mechanisms of S-MIF include isotopologue-dependent self-shielding, cross-sectional amplitudes, and vibronic coupling during intersystem crossing. This review discusses the emerging picture of the physical origins of S-MIF and their implications for the chemistry of the early Earth's atmosphere.

中文翻译:

二氧化硫的光化学和地球大气中与质量无关的同位素分馏的起源

太古代硫化物和硫酸盐矿物通常在四种稳定的硫同位素 32S、33S、34S 和 36S 之间表现出异常比例。这些异常关系,称为硫质量独立分馏(S-MIF),为早期缺氧大气提供了强有力的证据。在整个太古代的岩石中可以观察到三种同位素比率(δ33S、δ34S 和 δ36S)之间的相关变化,并且是确定 S-MIF 源反应的关键线索。迄今为止,关于太古代 S-MIF 起源的研究主要集中在二氧化硫 (SO2) 的光化学上。SO2 在波长 <220 nm 下的光解和在 240-340 nm 下的光激发都产生大幅度的 S-MIF。S-MIF 的拟议机制包括同位素体相关的自屏蔽、横截面振幅、和系统间交叉期间的振动耦合。这篇综述讨论了 S-MIF 物理起源的新图景及其对早期地球大气化学的影响。
更新日期:2017-08-30
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