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| Titel |
Multiple-sulfur isotope effects during photolysis of carbonyl sulfide |
| VerfasserIn |
Y. Lin, M. S. Sim, S. Ono |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 19 ; Nr. 11, no. 19 (2011-10-14), S.10283-10292 |
| Datensatznummer |
250010126
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| Publikation (Nr.) |
 copernicus.org/acp-11-10283-2011.pdf |
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| Zusammenfassung |
| Laboratory experiments were carried out to determine sulfur isotope effects
during ultraviolet photolysis of carbonyl sulfide (OCS) to carbon monoxide
(CO) and elemental sulfur (S0). The OCS gas at 3.7 to 501 mbar was
irradiated with or without a N2 bath gas using a 150 W Xe arc lamp.
Sulfur isotope ratios for the product S0 and residual OCS were analyzed
by an isotope ratio mass-spectrometer with SF6 as the analyte gas. The
isotope fractionation after correction for the reservoir effects is −6.8‰
for the ratio 34S/32S, where product S0 is depleted in heavy
isotopes. The magnitude of the overall isotope effect is not sensitive to
the addition of N2 but increases to −9.5‰ when radiation of λ > 285 nm is used. The measured isotope effect reflects that of photolysis as well
as the subsequent sulfur abstraction (from OCS) reaction. The magnitude of
isotope effects for the abstraction reaction is estimated by transition
state theory to be between −18.9 and −3.1‰ for 34S which gives the
photolysis isotope effect as −10.5 to +5.3‰. The observed triple isotope
coefficients are ln(δ34S + 1)/ln(δ34S + 1) = 0.534 ± 0.005 and
ln(δ36S + 1)/ln(δ34S + 1) = 1.980 ± 0.021. These values differ from
canonical values for mass-dependent fractionation of 0.515 and 1.90,
respectively. The result demonstrates that the OCS photolysis does not
produce large isotope effects of more than about 10‰ for 34S/32S,
and can be the major source of background stratospheric sulfate aerosol
(SSA) during volcanic quiescence. |
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