Multiple-sulfur isotope effects during photolysis of carbonyl sulfide
Laboratory experiments were carried out to determine sulfur isotope effects during ultraviolet photolysis of carbonyl sulfide (OCS) to carbon monoxide (CO) and elemental sulfur (S<sup>0</sup>). The OCS gas at 3.7 to 501 mbar was irradiated with or without a N<sub&a...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2011-10-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/11/10283/2011/acp-11-10283-2011.pdf |
| _version_ | 1811309197098221568 |
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| author | Y. Lin M. S. Sim S. Ono |
| author_facet | Y. Lin M. S. Sim S. Ono |
| author_sort | Y. Lin |
| collection | DOAJ |
| description | Laboratory experiments were carried out to determine sulfur isotope effects during ultraviolet photolysis of carbonyl sulfide (OCS) to carbon monoxide (CO) and elemental sulfur (S<sup>0</sup>). The OCS gas at 3.7 to 501 mbar was irradiated with or without a N<sub>2</sub> bath gas using a 150 W Xe arc lamp. Sulfur isotope ratios for the product S<sup>0</sup> and residual OCS were analyzed by an isotope ratio mass-spectrometer with SF<sub>6</sub> as the analyte gas. The isotope fractionation after correction for the reservoir effects is −6.8&permil; for the ratio <sup>34</sup>S/<sup>32</sup>S, where product S<sup>0</sup> is depleted in heavy isotopes. The magnitude of the overall isotope effect is not sensitive to the addition of N<sub>2</sub> but increases to −9.5&permil; when radiation of &lambda; > 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&permil; for <sup>34</sup>S which gives the photolysis isotope effect as −10.5 to +5.3&permil;. The observed triple isotope coefficients are ln(&delta;<sup>34</sup>S + 1)/ln(&delta;<sup>34</sup>S + 1) = 0.534 &plusmn; 0.005 and ln(&delta;<sup>36</sup>S + 1)/ln(&delta;<sup>34</sup>S + 1) = 1.980 &plusmn; 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&permil; for <sup>34</sup>S/<sup>32</sup>S, and can be the major source of background stratospheric sulfate aerosol (SSA) during volcanic quiescence. |
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| format | Article |
| id | doaj.art-9d0721bd81874db3a7751c7b6e87e490 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-04-13T09:36:48Z |
| publishDate | 2011-10-01 |
| publisher | Copernicus Publications |
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| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-9d0721bd81874db3a7751c7b6e87e4902022-12-22T02:52:03ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242011-10-011119102831029210.5194/acp-11-10283-2011Multiple-sulfur isotope effects during photolysis of carbonyl sulfideY. LinM. S. SimS. OnoLaboratory experiments were carried out to determine sulfur isotope effects during ultraviolet photolysis of carbonyl sulfide (OCS) to carbon monoxide (CO) and elemental sulfur (S<sup>0</sup>). The OCS gas at 3.7 to 501 mbar was irradiated with or without a N<sub>2</sub> bath gas using a 150 W Xe arc lamp. Sulfur isotope ratios for the product S<sup>0</sup> and residual OCS were analyzed by an isotope ratio mass-spectrometer with SF<sub>6</sub> as the analyte gas. The isotope fractionation after correction for the reservoir effects is −6.8&permil; for the ratio <sup>34</sup>S/<sup>32</sup>S, where product S<sup>0</sup> is depleted in heavy isotopes. The magnitude of the overall isotope effect is not sensitive to the addition of N<sub>2</sub> but increases to −9.5&permil; when radiation of &lambda; > 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&permil; for <sup>34</sup>S which gives the photolysis isotope effect as −10.5 to +5.3&permil;. The observed triple isotope coefficients are ln(&delta;<sup>34</sup>S + 1)/ln(&delta;<sup>34</sup>S + 1) = 0.534 &plusmn; 0.005 and ln(&delta;<sup>36</sup>S + 1)/ln(&delta;<sup>34</sup>S + 1) = 1.980 &plusmn; 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&permil; for <sup>34</sup>S/<sup>32</sup>S, and can be the major source of background stratospheric sulfate aerosol (SSA) during volcanic quiescence.http://www.atmos-chem-phys.net/11/10283/2011/acp-11-10283-2011.pdf |
| spellingShingle | Y. Lin M. S. Sim S. Ono Multiple-sulfur isotope effects during photolysis of carbonyl sulfide Atmospheric Chemistry and Physics |
| title | Multiple-sulfur isotope effects during photolysis of carbonyl sulfide |
| title_full | Multiple-sulfur isotope effects during photolysis of carbonyl sulfide |
| title_fullStr | Multiple-sulfur isotope effects during photolysis of carbonyl sulfide |
| title_full_unstemmed | Multiple-sulfur isotope effects during photolysis of carbonyl sulfide |
| title_short | Multiple-sulfur isotope effects during photolysis of carbonyl sulfide |
| title_sort | multiple sulfur isotope effects during photolysis of carbonyl sulfide |
| url | http://www.atmos-chem-phys.net/11/10283/2011/acp-11-10283-2011.pdf |
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