Photochemical and thermochemical pathways to S<sub>2</sub> and polysulfur formation in the atmosphere of Venus.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 35907911.
- Also identified by DOI 10.1038/s41467-022-32170-x and PMC identifier 9338966.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Polysulfur species have been proposed to be the unknown near-UV absorber in the atmosphere of Venus. Recent work argues that photolysis of one of the (SO)<sub>2</sub> isomers, cis-OSSO, directly yields S<sub>2</sub> with a branching ratio of about 10%. If correct, this pathway dominates polysulfur formation by several orders of magnitude, and by addition reactions yields significant quantities of S<sub>3</sub>, S<sub>4</sub>, and S<sub>8</sub>. We report here the results of high-level ab-initio quantum-chemistry computations that demonstrate that S<sub>2</sub> is not a product in cis-OSSO photolysis. Instead, we establish a novel mechanism in which S<sub>2</sub> is formed in a two-step process. Firstly, the intermediate S<sub>2</sub>O is produced by the coupling between the S and Cl atmospheric chemistries (in particular, SO reaction with ClS) and in a lesser extension by O-abstraction reactions from cis-OSSO. Secondly, S<sub>2</sub>O reacts with SO. This modified chemistry yields S<sub>2</sub> and subsequent polysulfur abundances comparable to the photolytic cis-OSSO mechanism through a more plausible pathway. Ab initio quantification of the photodissociations at play fills a critical data void in current atmospheric models of Venus.