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Photoabsorption cross‐section measurements of 32 S, 33 S, 34 S, and 36 S sulfur dioxide from 190 to 220 nm
Author(s) -
Endo Yoshiaki,
Danielache Sebastian O.,
Ueno Yuichiro,
Hattori Shohei,
Johnson Matthew S.,
Yoshida Naohiro,
Kjaergaard Henrik G.
Publication year - 2015
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2014jd021671
Subject(s) - isotopologue , photodissociation , analytical chemistry (journal) , absorption (acoustics) , chemistry , absorption spectroscopy , spectral line , absorption cross section , isotope , isotopic shift , atomic physics , cross section (physics) , physics , optics , photochemistry , nuclear physics , chromatography , quantum mechanics , astronomy
The ultraviolet absorption cross sections of the SO 2 isotopologues are essential to understanding the photochemical fractionation of sulfur isotopes in planetary atmospheres. We present measurements of the absorption cross sections of 32 SO 2 , 33 SO 2 , 34 SO 2 , and 36 SO 2 , recorded from 190 to 220 nm at room temperature with a resolution of 0.1 nm (~25 cm −1 ) made using a dual‐beam photospectrometer. The measured absorption cross sections show an apparent pressure dependence and a newly developed analytical model shows that this is caused by underresolved fine structure. The model made possible the calculation of absorption cross sections at the zero‐pressure limit that can be used to calculate photolysis rates for atmospheric scenarios. The 32 SO 2 , 33 SO 2 , and 34 SO 2 cross sections improve upon previously published spectra including fine structure and peak widths. This is the first report of absolute absorption cross sections of the 36 SO 2 isotopologue for the C 1 B 2 ‐ X 1 A 2 band where the amplitude of the vibrational structure is smaller than the other isotopologues throughout the spectrum. Based on the new results, solar UV photodissociation of SO 2 produces 34 ε , 33 Ε , and 36 Ε isotopic fractionations of +4.6 ± 11.6‰, +8.8 ± 9.0‰, and −8.8 ± 19.6‰, respectively. From these spectra isotopic effects during photolysis in the Archean atmosphere can be calculated and compared to the Archean sedimentary record. Our results suggest that broadband solar UV photolysis is capable of producing the mass‐independent fractionation observed in the Archean sedimentary record without involving shielding by specific gaseous compounds in the atmosphere including SO 2 itself. The estimated magnitude of 33 Ε , for example, is close to the maximum Δ 33 S observed in the geological record.