Mass-independent fractionation of sulfur isotopes by isotope-selective photodissociation of SO2

James R. Lyons

Research output: Contribution to journalArticlepeer-review

88 Scopus citations


A quantitative understanding the origin of sulfur isotope mass-independent fractionation (MIF) is essential to a full interpretation of the Archean sulfur geochemical record. Laboratory experiments have demonstrated that a MIF signature is present in elemental sulfur produced during SO2 photolysis, but the underlying mechanism remains unknown. Here, I report the results of atmospheric chemistry modeling of isotope-selective photodissociation of SO2 in the C1B2 - X1A1 bands from 190 to 220 nm. This band system is dominated by a bending mode progression that produces shifts in the absorption spectrum upon sulfur isotope substitution. Self-shielding in the rotationally-resolved lines of 32SO2 produces MIF signatures in SO and residual SO2. A self-shielding origin for sulfur MIF implies that the variations observed in Δ33S in Archean rocks reflect variation in atmospheric SO2 concentration, and demonstrates that MIF: in terrestrial rocks can be derived from photochemistry independent of molecular symmetry.

Original languageEnglish (US)
Article numberL22811
JournalGeophysical Research Letters
Issue number22
StatePublished - Nov 28 2007
Externally publishedYes

ASJC Scopus subject areas

  • Geophysics
  • Earth and Planetary Sciences(all)


Dive into the research topics of 'Mass-independent fractionation of sulfur isotopes by isotope-selective photodissociation of SO2'. Together they form a unique fingerprint.

Cite this