Photopolymerization and Mass-Independent Sulfur Isotope Fractionations in Carbon Disulfide

Colman, Jonah J.; Xu, Xianping; Thiemens, M. H.; Trogler, William C.

doi:10.1126/science.273.5276.774

Cited by 55 publications

(43 citation statements)

References 21 publications

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“…In particular, pairs of levels capable of interacting with each other and that are near-degenerate for one isotopologue may be nondegenerate for other isotopologues. These effects were cited previously as a source of S-MIF during the photopolymerization of CS 2 (41,42) and oxygen MIF during the photodissociation of CO 2 (43) and CO (44). In these three cases, the anomalous isotope effects have been attributed to differences in intersystem crossing (ISC) rates from an initially excited singlet state to a reactive (or dissociative) triplet state.…”

Section: Results Of Photochemical Experimentsmentioning

confidence: 99%

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO₂and the implications to the early earth’s atmosphere

Whitehill

Xie

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Signatures of mass-independent isotope fractionation (MIF) † Significant deviations from these mass-dependent scaling laws are referred to as mass-independent fractionation (MIF), and serve as important tracers in the earth and planetary sciences (see refs. 3-5).Early studies suggested that MIF could result only from nucleosynthetic processes (6), and the earliest measurements of oxygen MIF in calcium-aluminum inclusions of meteorites originally were interpreted to be nucleosynthetic in origin (7). It eventually was suggested (8) that chemical processes, such as tunneling or processes associated with predissociation, also might produce MIF. The first experimental evidence for a chemical origin of MIF came from ozone generated by an electric discharge or UV radiation (9, 10). The discovery of oxygen MIF in stratospheric ozone (11) soon triggered intense research into the physiochemical origin of MIF in the ozone system (see refs. 12-14). The possible chemical origins of MIF signatures still are poorly understood.For the sulfur isotope system ( 32 S, 33 S, 34 S, and 36 S), Farquhar et al. (15) made the remarkable discovery that mass-independent sulfur isotope fractionation (S-MIF) is prevalent in sedimentary rocks older than ca. 2.4 Ga but absent in rocks from subsequent periods. The disappearance of S-MIF at about 2.4 Ga (16, 17) signifies a fundamental change in the earth's surface sulfur cycles, and generally is linked to the suppression of both SO 2 photolysis and the formation of elemental sulfur aerosols by the rise of atmospheric oxygen levels (15,18,19). The Archean S-MIF is considered the most compelling evidence for an anoxic early atmosphere and constrains Archean oxygen levels to be less than 10−5 of present levels (19). This model of oxygen evolution, however, depends critically on the assumption that UV photolysis of SO 2 by ∼200 nm radiation is the ultimate source of the anomalous sulfur isotope signature (18). Constraining the source of the S-MIF requires a thorough understanding of the physiochemical origins of S-MIF during the photochemistry of SO 2 .SO 2 exhibits two strong absorption band systems in the UV region: one between 185 nm and 235 nm (C 1 B 2 ←X

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Section: Results Of Photochemical Experimentsmentioning

confidence: 99%

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO₂and the implications to the early earth’s atmosphere

Whitehill

Xie

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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“…[33] Research done to date has been largely exploratory and includes studies of photolysis of SO 2 and H 2 S [Farquhar et al, 2000b[Farquhar et al, , 2001] and photopolymerization of CS and CS 2 [Colman et al, 1996;Zmolek et al, 1999] Romero and Thiemens, 2003;Savarino et al, 2003;Baroni et al, 2007] and the requirement of short wavelengths has cited the reactions that produce the effects in the stratosphere. Note that the reactions that produce the effect may be related to sulfur dioxide, or they may be related to photolysis of long-lived bound states (or intermediates) [Farquhar et al, 2001;Lyons, 2008].…”

Section: Mechanisms For Producing Mass-independent Sulfur Isotope Anomentioning

confidence: 99%

Identification of sources and formation processes of atmospheric sulfate by sulfur isotope and scanning electron microscope measurements

et al. 2010

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[1] Atmospheric sulfate aerosols have a cooling effect on the Earth's surface and can change cloud microphysics and precipitation. China has heavy loading of sulfate, but their sources and formation processes remain uncertain. In this study we characterize possible sources and formation processes of atmospheric sulfate by analyzing sulfur isotope abundances ( 32 S, 33 S, 34 S, and 36 S) and by detailed X-ray diffraction and scanning electron microscope (SEM) imaging of aerosol samples acquired at a rural site in northern China from March to August 2005. The comparison of SEM images from coal fly ash and the atmospheric aerosols suggests that direct emission from coal combustion is a substantial source of primary atmospheric sulfate in the form of CaSO 4 . Airborne gypsum (CaSO 4 ·2H 2 O) is usually attributed to eolian dust or atmospheric reactions with H 2 SO 4 . SEM imaging also reveals mineral particles with soot aggregates adhered to the surface where they could decrease the single scattering albedo of these aerosols. In summer months, heterogeneous oxidation of SO 2 , derived from coal combustion, appears to be the dominant source of atmospheric sulfate. Our analyses of aerosol sulfate show a seasonal variation in D 33 S (D 33 S describes either a 33 S excess or depletion relative to that predicted from consideration of classical mass-dependent isotope effects). Similar sulfur isotope variations have been observed in other atmospheric samples and in (homogenous) gas-phase reactions. On the basis of atmospheric sounding and satellite data as well as a possible relationship between D 33 S and Convective Available Potential Energy (CAPE) during the sampling period, we attribute the sulfur isotope anomalies (D 33 S and D 36 S) in Xianghe aerosol sulfates to another atmospheric source (upper troposphere or lower stratosphere).Citation: Guo, Z., Z. Li, J. Farquhar, A. J. Kaufman, N. Wu, C. Li, R. R. Dickerson, and P. Wang (2010), Identification of sources and formation processes of atmospheric sulfate by sulfur isotope and scanning electron microscope measurements,

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“…These studies, and others related to enrichment, have been made in ozone in the atmosphere, [3][4][5][6][7][8][9][10][11][12] the laboratory, in other molecules, 28,[36][37][38][39] and in ions. [40][41][42][43] In this unusual effect in a chemical reaction, the enrichment or depletion of two isotopes relative to that of a third is equal.…”

Section: Introductionmentioning

confidence: 99%

An intramolecular theory of the mass-independent isotope effect for ozone. I

Hathorn

Marcus

1999

The Journal of Chemical Physics

125

147

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An intramolecular theory of the unusual mass-independent isotope effect for ozone formation and dissociation is described. The experiments include the enrichment factor, its dependence on the ambient pressure, the ratio of the formation rates of symmetric and asymmetric ozone isotopomers, the enrichment of ozone formed from heavily enriched oxygen isotopes, the comparison of that enrichment to that when the heavy isotopes are present in trace amounts, the isotopic exchange rate constant, and the large mass-dependent effect when individual rate constants are measured, in contrast with the mass-independent effect observed for scrambled mixtures. To explain the results it is suggested that apart from the usual symmetry number ratio of a factor of 2, the asymmetric ozone isotopomers have a larger density of reactive ͑coupled͒ quantum states, compared with that for the symmetric isotopomers ͑about 10%͒, due to being more ''RRKM-like'' ͑Rice-RamspergerKessel-Marcus͒: Symmetry restricts the number of intramolecular resonances and coupling terms in the Hamiltonian which are responsible for making the motion increasingly chaotic and, thereby, increasingly statistical. As a result the behavior occurs regardless of whether the nuclei are bosons ( . Two alternative mechanisms are also considered, one invoking excited electronic states and the other invoking symmetry control in the entrance channel. Arguments against each are given. An expression is given relating the mass-independent rates of the scrambled systems to the mass-dependent rates of the unscrambled ones, and the role played by a partitioning term in the latter is described. Different definitions for the enrichment factor for heavily enriched isotopic systems are also considered. In the present paper attention is focused on setting up theoretical expressions and discussing relationships. They provide a basis for future detailed calculations.

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Photopolymerization and Mass-Independent Sulfur Isotope Fractionations in Carbon Disulfide

Cited by 55 publications

References 21 publications

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO₂and the implications to the early earth’s atmosphere

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO₂and the implications to the early earth’s atmosphere

Identification of sources and formation processes of atmospheric sulfate by sulfur isotope and scanning electron microscope measurements

An intramolecular theory of the mass-independent isotope effect for ozone. I

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Photopolymerization and Mass-Independent Sulfur Isotope Fractionations in Carbon Disulfide

Cited by 55 publications

References 21 publications

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO2and the implications to the early earth’s atmosphere

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO2and the implications to the early earth’s atmosphere

Identification of sources and formation processes of atmospheric sulfate by sulfur isotope and scanning electron microscope measurements

An intramolecular theory of the mass-independent isotope effect for ozone. I

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Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO₂and the implications to the early earth’s atmosphere

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO₂and the implications to the early earth’s atmosphere