Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO[subscript 2] and the implications to the early earth's atmosphere
Signatures of mass-independent isotope fractionation (MIF) are found in the oxygen ([superscript 16]O, [superscript 17]O, [superscript 18]O) and sulfur ([superscript 32]S, [superscript 33]S, [superscript 34]S, [superscript 36]S) isotope systems and serve as important tracers of past and present atmo...
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| Format: | Article |
| Language: | en_US |
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National Academy of Sciences (U.S.)
2014
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| Online Access: | http://hdl.handle.net/1721.1/85909 https://orcid.org/0000-0001-5996-8217 https://orcid.org/0000-0002-1348-9584 |
| _version_ | 1811092298742628352 |
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| author | Whitehill, Andrew Richard Ono, Shuhei Xie, Changjian Hu, Xixi Xie, Daiqian Guo, Hua |
| author2 | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences |
| author_facet | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Whitehill, Andrew Richard Ono, Shuhei Xie, Changjian Hu, Xixi Xie, Daiqian Guo, Hua |
| author_sort | Whitehill, Andrew Richard |
| collection | MIT |
| description | Signatures of mass-independent isotope fractionation (MIF) are found in the oxygen ([superscript 16]O, [superscript 17]O, [superscript 18]O) and sulfur ([superscript 32]S, [superscript 33]S, [superscript 34]S, [superscript 36]S) isotope systems and serve as important tracers of past and present atmospheric processes. These unique isotope signatures signify the breakdown of the traditional theory of isotope fractionation, but the physical chemistry of these isotope effects remains poorly understood. We report the production of large sulfur isotope MIF, with Δ[superscript 33]S up to 78‰ and Δ[superscript 36]S up to 110‰, from the broadband excitation of SO[subscript 2] in the 250–350-nm absorption region. Acetylene is used to selectively trap the triplet-state SO[subscript 2] ([~ over a][superscript 3]B[subscript 1]), which results from intersystem crossing from the excited singlet ([~ over A][superscript 1]A[subscript 2]/[~ over B][superscript 1]B[subscript 1]) states. The observed MIF signature differs considerably from that predicted by isotopologue-specific absorption cross-sections of SO[subscript 2] and is insensitive to the wavelength region of excitation (above or below 300 nm), suggesting that the MIF originates not from the initial excitation of SO[subscript 2] to the singlet states but from an isotope selective spin–orbit interaction between the singlet ([~ over A][superscript 1]A[subscript 2]/[~ over B][superscript 1]B[subscript 1]) and triplet ([~ over a][superscript 3]B[subscript 1]) manifolds. Calculations based on high-level potential energy surfaces of the multiple excited states show a considerable lifetime anomaly for [superscript 33]SO[subscript 2] and [superscript 36]SO[subscript 2] for the low vibrational levels of the [~ over A][superscript 1]A[subscript 2] state. These results demonstrate that the isotope selectivity of accidental near-resonance interactions between states is of critical importance in understanding the origin of MIF in photochemical systems. |
| first_indexed | 2024-09-23T15:16:07Z |
| format | Article |
| id | mit-1721.1/85909 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T15:16:07Z |
| publishDate | 2014 |
| publisher | National Academy of Sciences (U.S.) |
| record_format | dspace |
| spelling | mit-1721.1/859092022-09-29T13:46:40Z Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO[subscript 2] and the implications to the early earth's atmosphere Whitehill, Andrew Richard Ono, Shuhei Xie, Changjian Hu, Xixi Xie, Daiqian Guo, Hua Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Whitehill, Andrew Richard Ono, Shuhei Signatures of mass-independent isotope fractionation (MIF) are found in the oxygen ([superscript 16]O, [superscript 17]O, [superscript 18]O) and sulfur ([superscript 32]S, [superscript 33]S, [superscript 34]S, [superscript 36]S) isotope systems and serve as important tracers of past and present atmospheric processes. These unique isotope signatures signify the breakdown of the traditional theory of isotope fractionation, but the physical chemistry of these isotope effects remains poorly understood. We report the production of large sulfur isotope MIF, with Δ[superscript 33]S up to 78‰ and Δ[superscript 36]S up to 110‰, from the broadband excitation of SO[subscript 2] in the 250–350-nm absorption region. Acetylene is used to selectively trap the triplet-state SO[subscript 2] ([~ over a][superscript 3]B[subscript 1]), which results from intersystem crossing from the excited singlet ([~ over A][superscript 1]A[subscript 2]/[~ over B][superscript 1]B[subscript 1]) states. The observed MIF signature differs considerably from that predicted by isotopologue-specific absorption cross-sections of SO[subscript 2] and is insensitive to the wavelength region of excitation (above or below 300 nm), suggesting that the MIF originates not from the initial excitation of SO[subscript 2] to the singlet states but from an isotope selective spin–orbit interaction between the singlet ([~ over A][superscript 1]A[subscript 2]/[~ over B][superscript 1]B[subscript 1]) and triplet ([~ over a][superscript 3]B[subscript 1]) manifolds. Calculations based on high-level potential energy surfaces of the multiple excited states show a considerable lifetime anomaly for [superscript 33]SO[subscript 2] and [superscript 36]SO[subscript 2] for the low vibrational levels of the [~ over A][superscript 1]A[subscript 2] state. These results demonstrate that the isotope selectivity of accidental near-resonance interactions between states is of critical importance in understanding the origin of MIF in photochemical systems. Exobiology Program (U.S.) (Grant NNX10AR85G) 2014-03-24T17:24:14Z 2014-03-24T17:24:14Z 2013-07 2013-04 Article http://purl.org/eprint/type/JournalArticle 0027-8424 1091-6490 http://hdl.handle.net/1721.1/85909 Whitehill, A. R., C. Xie, X. Hu, D. Xie, H. Guo, and S. Ono. “Vibronic Origin of Sulfur Mass-Independent Isotope Effect in Photoexcitation of SO2 and the Implications to the Early Earth’s Atmosphere.” Proceedings of the National Academy of Sciences 110, no. 44 (October 29, 2013): 17697–17702. https://orcid.org/0000-0001-5996-8217 https://orcid.org/0000-0002-1348-9584 en_US http://dx.doi.org/10.1073/pnas.1306979110 Proceedings of the National Academy of Sciences Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf National Academy of Sciences (U.S.) National Academy of Science (U.S.) |
| spellingShingle | Whitehill, Andrew Richard Ono, Shuhei Xie, Changjian Hu, Xixi Xie, Daiqian Guo, Hua Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO[subscript 2] and the implications to the early earth's atmosphere |
| title | Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO[subscript 2] and the implications to the early earth's atmosphere |
| title_full | Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO[subscript 2] and the implications to the early earth's atmosphere |
| title_fullStr | Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO[subscript 2] and the implications to the early earth's atmosphere |
| title_full_unstemmed | Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO[subscript 2] and the implications to the early earth's atmosphere |
| title_short | Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO[subscript 2] and the implications to the early earth's atmosphere |
| title_sort | vibronic origin of sulfur mass independent isotope effect in photoexcitation of so subscript 2 and the implications to the early earth s atmosphere |
| url | http://hdl.handle.net/1721.1/85909 https://orcid.org/0000-0001-5996-8217 https://orcid.org/0000-0002-1348-9584 |
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