Experimental and theoretical exploration of photodissociation of SO2 via the C̃1B2 state: identification of the dissociation pathway

Katagiri, Hideki; Sako, Takeshi; Hishikawa, Akiyoshi; Yazaki, Takeki; Onda, Ken; Yamanouchi, Kaoru; Yoshino, K.

doi:10.1016/s0022-2860(97)00199-3

Cited by 88 publications

(150 citation statements)

References 52 publications

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“…In the 165 to 235 nm wavelength region, SO 2 photolysis occurs through pre-dissociation from the bound C( 1 B 2 ) state. Near the dissociation threshold of 218.7 nm (Becker et al, 1995), the quantum yield of photolysis is less than unity, although it increases to greater than 0.99 at wavelengths shorter than 215 nm (Katagiri et al, 1997). In the region where the quantum yield is close to unity (i.e., less than 215 nm), the isotope effects due to SO 2 photolysis should be determined entirely by the differences in the absorption cross sections between the different isotopologues of SO 2 (e.g., by isotopologue specific Franck-Condon coupling) ( Potential energy profiles on the singlet (red) and triplet (blue) potential energy surfaces for the SO 3 system obtained using B3LYP optimization followed by UCCSD(T)-F12a single point calculation, with the aug-cc-pVTZ basis set.…”

Section: Origin Of Mass-independent Fractionation During So 2 Photochmentioning

confidence: 95%

“…In the narrow spectral region from 215 to 218.7 nm, where the quantum yield of photodissociation varies, it is possible that quantum yield differences between isotopologues could potentially produce additional isotope effects beyond those predicted from absorption cross sections. However, in this region, photodissociation occurs primarily via vibronic mixing of the C( 1 B 2 ) state levels with dissociative continuum of the electronic ground, X( 1 A 1 ) state (Katagiri et al, 1997). Due to the high density of vibronic levels for the X( 1 A 1 ) state, it is unlikely that there will be significant isotope effects in the coupling strength between the C( 1 B 2 ) and X( 1 A 1 ) states.…”

Section: Origin Of Mass-independent Fractionation During So 2 Photochmentioning

confidence: 99%

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SO<sub>2</sub> photolysis as a source for sulfur mass-independent isotope signatures in stratospehric aerosols

et al. 2015

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Abstract. Signatures of sulfur isotope mass-independent fractionation (S-MIF) have been observed in stratospheric sulfate aerosols deposited in polar ice. The S-MIF signatures are thought to be associated with stratospheric photochemistry following stratospheric volcanic eruptions, but the exact mechanism responsible for the production and preservation of these signatures is debated. In order to identify the origin and the mechanism of preservation for these signatures, a series of laboratory photochemical experiments were carried out to investigate the effect of temperature and added O 2 on the S-MIF produced by two absorption band systems of SO 2 : photolysis in the 190 to 220 nm region and photoexcitation in the 250 to 350 nm region. The SO 2 photolysis (SO 2 + hν → SO+O) experiments showed S-MIF signals with large 34 S/ 32 S fractionations, which increases with decreasing temperature. The overall S-MIF pattern observed for photolysis experiments, including high 34 S/ 32 S fractionations, positive mass-independent anomalies in 33 S, and negative anomalies in 36 S, is consistent with a major contribution from optical isotopologue screening effects and data for stratospheric sulfate aerosols. In contrast, SO 2 photoexcitation produced products with positive S-MIF anomalies in both 33 S and 36 S, which is different from stratospheric sulfate aerosols. SO 2 photolysis in the presence of O 2 produced SO 3 with S-MIF signals, suggesting the transfer of the S-MIF anomalies from SO to SO 3 by the SO + O 2 + M → SO 3 + M reaction. This is supported with energy calculations of stationary points on the SO 3 potential energy surfaces, which indicate that this reaction occurs slowly on a single adiabatic surface, but that it can occur more rapidly through intersystem crossing. Based on our experimental results, we estimate a termolecular rate constant on the order of 10 −37 cm 6 molecule −2 s −1 . This rate can explain the preservation of mass independent isotope signatures in stratospheric sulfate aerosols and provides a minor, but important, oxidation pathway for stratospheric SO 2 . The production and preservation of S-MIF signals requires a high SO 2 column density to allow for optical isotopologue screening effects to occur and to generate a large enough signature that it can be preserved. In addition, the SO 2 plume must reach an altitude of around 20 to 25 km, where SO 2 photolysis becomes a dominant process. These experiments are the first step towards understanding the origin of the sulfur isotope anomalies in stratospheric sulfate aerosols.

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Section: Origin Of Mass-independent Fractionation During So 2 Photochmentioning

confidence: 95%

Section: Origin Of Mass-independent Fractionation During So 2 Photochmentioning

confidence: 99%

SO<sub>2</sub> photolysis as a source for sulfur mass-independent isotope signatures in stratospehric aerosols

et al. 2015

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“…Panels (a) and (b) show the singlet and triplet state ionisation pathways, respectively. The schematic diabatic potential energy curves were adapted from the results of the ab initio calculations with the exception of the (2) 1 A 1 state which was adapted from the works of Kamiya and Matsui 8 and Katagiri et al 93 In contrast to the other potential curves shown, this surface represents the adiabatic potential leading to the first 1 u state at linearity. The ionisation pathways thought to lead to SO + 2 photoelectron bands (1), (2), (3), and (1 ) are denoted by the "e − (1)," "e − (2)," "e − (3)," and "e − (1 )" arrows, respectively.…”

Section: Overviewmentioning

confidence: 99%

Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy

Wilkinson

Boguslavskiy

Mikosch

et al. 2014

The Journal of Chemical Physics

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The excited state dynamics of isolated sulfur dioxide molecules have been investigated using the time-resolved photoelectron spectroscopy and time-resolved photoelectron-photoion coincidence techniques. Excited state wavepackets were prepared in the spectroscopically complex, electronically mixed (${\tilde{\rm B}}$B̃)1B1/(Ã)1A2, Clements manifold following broadband excitation at a range of photon energies between 4.03 eV and 4.28 eV (308 nm and 290 nm, respectively). The resulting wavepacket dynamics were monitored using a multiphoton ionisation probe. The extensive literature associated with the Clements bands has been summarised and a detailed time domain description of the ultrafast relaxation pathways occurring from the optically bright (${\tilde{\rm B}}$B̃)1B1 diabatic state is presented. Signatures of the oscillatory motion on the (${\tilde{\rm B}}$B̃)1B1/(Ã)1A2 lower adiabatic surface responsible for the Clements band structure were observed. The recorded spectra also indicate that a component of the excited state wavepacket undergoes intersystem crossing from the Clements manifold to the underlying triplet states on a sub-picosecond time scale. Photoelectron signal growth time constants have been predominantly associated with intersystem crossing to the (${\tilde{\rm c}}$c̃)3B2 state and were measured to vary between 750 and 150 fs over the implemented pump photon energy range. Additionally, pump beam intensity studies were performed. These experiments highlighted parallel relaxation processes that occurred at the one- and two-pump-photon levels of excitation on similar time scales, obscuring the Clements band dynamics when high pump beam intensities were implemented. Hence, the Clements band dynamics may be difficult to disentangle from higher order processes when ultrashort laser pulses and less-differential probe techniques are implemented.

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“…Isotope effects due primarily to absorption, as predicted by isotopologue-specific cross-sections, do not contribute significantly to the large S-MIF observed, particularly in 36 S. Rapid vibrational relaxation allows expression of S-MIF signatures from localized accidental degeneracies regardless of the initially excited vibronic level. The same mechanism, however, may not be applied to the 180-and 220-nm band systems of SO 2 because the quantum efficiency of photolysis is near unity below 205 nm (59), and the lifetime is sufficiently short that little vibrational relaxation occurs. Although the S-MIF signatures observed in this study, particularly the Δ 36 S/Δ 33 S ratios, do not match those from the Archean, the photochemistry in the photoexcitation band can produce large mass-independent signatures (i.e., Δ 33 S values) with relatively small mass-dependent fractionations (i.e., δ 34 S values), which is necessary to explain the preservation of large Archean S-MIF signatures.…”

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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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Experimental and theoretical exploration of photodissociation of SO2 via the C̃1B2 state: identification of the dissociation pathway

Cited by 88 publications

References 52 publications

SO<sub>2</sub> photolysis as a source for sulfur mass-independent isotope signatures in stratospehric aerosols

SO<sub>2</sub> photolysis as a source for sulfur mass-independent isotope signatures in stratospehric aerosols

Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy

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

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Experimental and theoretical exploration of photodissociation of SO2 via the C̃1B2 state: identification of the dissociation pathway

Cited by 88 publications

References 52 publications

SO&lt;sub&gt;2&lt;/sub&gt; photolysis as a source for sulfur mass-independent isotope signatures in stratospehric aerosols

SO&lt;sub&gt;2&lt;/sub&gt; photolysis as a source for sulfur mass-independent isotope signatures in stratospehric aerosols

Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy

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

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Product

Resources

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SO<sub>2</sub> photolysis as a source for sulfur mass-independent isotope signatures in stratospehric aerosols

SO<sub>2</sub> photolysis as a source for sulfur mass-independent isotope signatures in stratospehric aerosols

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