Electronic Spectra of Carbonyl Sulfide Sulfur Isotopologues

Abstract

Carbonyl sulfide (OCS), a relatively inert tropospheric species that photolyzes into CO + S upon reaching the stratosphere, is deemed a significant contributor to background sulfate aerosol. A recent analysis of atmospheric infrared transmittance data has revealed that OC^(34)S is preferentially depleted above ~10 km. We now report that the OC^(34)S absorption band between 200 ≤ λ [nm] ≤ 260 at 298 K is broader and more intense than its OC^(32)S counterpart. This finding is consistent with the faster photolysis of OC^(34)S, and with a time-dependent formulation of electronic spectra. Since OCS photolysis in the lower stratosphere occurs in a spectral range in which its absorption cross-section is unaffected by temperature, we are able to estimate a ^(34)S-enrichment factor <^(34)ε> ~ (67 ± 7)‰ for this process that is commensurate with the value previously inferred from OC^(34)S/OC^(32)S ratio versus altitude profiles.

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