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| Titel |
Ultraviolet absorption cross sections of carbonyl sulfide isotopologues OC32S, OC33S, OC34S and O13CS: isotopic fractionation in photolysis and atmospheric implications |
| VerfasserIn |
S. Hattori, S. O. Danielache, M. S. Johnson, J. A. Schmidt, H. G. Kjaergaard, S. Toyoda, Y. Ueno, N. Yoshida |
| 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.10293-10303 |
| Datensatznummer |
250010127
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| Publikation (Nr.) |
 copernicus.org/acp-11-10293-2011.pdf |
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| Zusammenfassung |
| We report measurements of the ultraviolet absorption cross sections of
OC32S, OC33S, OC34S and O13CS from 195 to 260 nm. The
OCS isotopologues were synthesized from isotopically-enriched elemental
sulfur by reaction with carbon monoxide. The measured cross section of
OC32S is consistent with literature spectra recorded using natural
abundance samples. Relative to the spectrum of the most abundant
isotopologue, substitution of heavier rare isotopes has two effects. First,
as predicted by the reflection principle, the Gaussian-based absorption
envelope becomes slightly narrower and blue-shifted. Second, as predicted
by Franck-Condon considerations, the weak vibrational structure is
red-shifted. Sulfur isotopic fractionation constants (33ε,
34ε) as a function of wavelength are not highly structured, and tend to
be close to zero on average on the high energy side and negative on the low energy side.
The integrated photolysis rate of each isotopologue at 20 km, the approximate altitude at
which most OCS photolysis occurs, was calculated.
Sulfur isotopic fractionation constants at 20 km altitude are (−3.7 ± 4.5)‰ and
(1.1 ± 4.2)‰ for 33ε and 34ε, respectively, which is
inconsistent with the previously estimated large fractionation of over
73‰ in 34ε. This demonstrates that OCS photolysis does not produce sulfur
isotopic fractionation of more than ca. 5‰, suggesting OCS may indeed be a significant source
of background stratospheric sulfate aerosols. Finally, the predicted
isotopic fractionation constant for 33S excess (33E) in OCS
photolysis is (−4.2 ± 6.6)‰, and thus photolysis of OCS is not expected
to be the source of the non-mass-dependent signature observed in modern and
Archaean samples. |
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