Carbonyl sulfide isotopologues: Ultraviolet absorption cross sections and stratospheric photolysis

Danielache, Sebastian O.; Nanbu, Shinkoh; Eskebjerg, Carsten; Johnson, Matthew S.; Yoshida, Naohiro

doi:10.1063/1.3156314

Cited by 25 publications

(40 citation statements)

References 38 publications

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“…The TDMs for the two 1 A states are much smaller than μ A and therefore the contributions of these states to the absorption cross section are small. The TDMs μ A and μ B calculated by Suzuki et al 26 and Danielache et al 40 are qualitatively and quantitatively similar to those shown in Fig. 8.…”

Section: Transition Dipole Moment Functionssupporting

confidence: 73%

“…10) and in striking contrast to N 2 O, σ A , and σ B are completely smooth. The calculated A state cross section of Suzuki et al 26 shows very intense and very dense structure, while the cross section calculated by Danielache et al 40 shows almost no structure except at high excitation energies at the edge of the absorption band (E ph > 49 000 cm −1 ). In the present study, only the cross sections for the quasi-bound states C, c, and d show vibrational resonance structure.…”

Section: B State-resolved Cross Sectionsmentioning

confidence: 91%

“…These surfaces were used to calculate the UV cross section and the product state distributions. In a more recent theoretical study 40 new global PESs and TDM functions were calculated in an attempt to evaluate the sulfur and carbon isotopic dependences of the absorption cross section. These previous investigations were helpful in describing the gross features of the dissociation dynamics, but rather large discrepancies remain between the experimentally observed absorption spectrum, isotope effects and product rotational state distributions and the corresponding theoretical predictions.…”

Section: Introductionmentioning

confidence: 99%

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The ultraviolet spectrum of OCS from first principles: Electronic transitions, vibrational structure and temperature dependence

Schmidt

Johnson

McBane

et al. 2012

The Journal of Chemical Physics

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Global three dimensional potential energy surfaces and transition dipole moment functions are calculated for the lowest singlet and triplet states of carbonyl sulfide at the multireference configuration interaction level of theory. The first ultraviolet absorption band is then studied by means of quantum mechanical wave packet propagation. Excitation of the repulsive 2 1 A state gives the main contribution to the cross section. Excitation of the repulsive 1 1 A state is about a factor of 20 weaker at the absorption peak (E ph ≈ 45 000 cm −1 ) but becomes comparable to the 2 1 A state absorption with decreasing energy (35 000 cm −1 ) and eventually exceeds it. Direct excitation of the repulsive triplet states is negligible except at photon energies E ph < 38 000 cm −1 . The main structure observed in the cross section is caused by excitation of the bound 2 3 A state, which is nearly degenerate with the 2 1 A state in the Franck-Condon region. The structure observed in the low energy tail of the spectrum is caused by excitation of quasi-bound bending vibrational states of the 2 1 A and 1 1 A electronic states. The absorption cross sections agree well with experimental data and the temperature dependence of the cross section is well reproduced.

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Section: Transition Dipole Moment Functionssupporting

confidence: 73%

Section: B State-resolved Cross Sectionsmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

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The ultraviolet spectrum of OCS from first principles: Electronic transitions, vibrational structure and temperature dependence

Schmidt

Johnson

McBane

et al. 2012

The Journal of Chemical Physics

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“…Jørgensen et al (2008) used the potential energy surfaces of Suzuki et al (1998) and found that 34 S enrichment is very small. A similar result was obtained by Danielache et al (2009) using different potential energy surfaces. The latter study also considered 13 C fractionation and found photolysis to greately deplete OCS in 13 C which contradicts recent experimental results of Hattori et al (2011).…”

Section: Introductionsupporting

confidence: 73%

OCS photolytic isotope effects from first principles: sulfur and carbon isotopes, temperature dependence and implications for the stratosphere

et al. 2013

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The isotopic fractionation in OCS photolysis is studied theoretically from first principles. UV absorption cross sections for OCS, OC33S, OC34S, OC36S and O13CS are calculated using the time-depedent quantum mechanical formalism and a recently developed ab-initio description of the photodissociation of OCS which takes into account the lowest four singlet and lowest four triplet electronic states. The calculated isotopic fractionations as a function of wavelength are in good agreement with recent measurements by Hattori et al. (2011) and indicate that photolysis leads to only a small enrichment of 34S in the remaining OCS. The photodissociation dynamics provide strong evidence that the photolysis quantum yield is unity at all wavelengths for atmospheric UV excitation, for all isotopologues. A simple stratospheric model is constructed taking into account the main sink reactions of OCS and it is found that overall stratospheric removal slightly favors light OCS in constrast to the findings of Leung et al. (2002). These results show, based on isotopic considerations, that OCS is an acceptable source of background stratosperic sulfate aerosol in agreement with a recent model study of of Brühl et al. (2012). The 13C isotopic fractionation due to photolysis of OCS in the upper stratosphere is significant and will leave a clear signal in the remaining OCS making it a candidate for tracing using the ACE-FTS and MIPAS data sets

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“…In the model, no isotopic fractionation is assumed for any reactions except for SO2 photolysis, for example, OCS photolysis is not associated with large isotopic fractionation (37). This assumption is probably not correct, although SO2 photolysis is often the rate limiting step for sulfate production in a reducing atmosphere, and hence likely controls the isotopic composition of aerosols (2)(3)(4)(5).…”

Section: Atmospheric Composition ( )mentioning

confidence: 99%

Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox

Ueno

Johnson

Danielache

et al. 2009

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

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144

124

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Distributions of sulfur isotopes in geological samples would provide a record of atmospheric composition if the mechanism producing the isotope effects could be described quantitatively. We determined the UV absorption spectra of 32 SO2, 33 SO2, and 34 SO2 and use them to interpret the geological record. The calculated isotopic fractionation factors for SO2 photolysis give mass independent distributions that are highly sensitive to the atmospheric concentrations of O 2, O3, CO2, H2O, CS2, NH3, N2O, H2S, OCS, and SO 2 itself. Various UV-shielding scenarios are considered and we conclude that the negative ⌬ 33 S observed in the Archean sulfate deposits can only be explained by OCS shielding. Of relevant Archean gases, OCS has the unique ability to prevent SO 2 photolysis by sunlight at >202 nm. Scenarios run using a photochemical box model show that ppm levels of OCS will accumulate in a CO-rich, reducing Archean atmosphere. The radiative forcing, due to this level of OCS, is able to resolve the faint young sun paradox. Further, the decline of atmospheric OCS may have caused the late Archean glaciation. mass independent fractionation ͉ carbonyl sulfide (OCS) ͉ sulfur dioxide (SO2) ͉ photochemistry ͉ greenhouse gases M ass independent fractionation (MIF) of sulfur isotopes has been found in geological samples older than 2.3 billion years (Ga) and is believed to be produced by the photochemical reactions of gaseous sulfur compounds in a low-oxygen reducing atmosphere (1-4). The rise of atmospheric oxygen (O 2 and O 3 ) would have oxidized atmospheric sulfur compounds to sulfate, preventing the accumulation of isotopic fractionation in two reservoirs. Moreover, it would have blocked UV sunlight inhibiting the supposed photochemical process(es) producing the isotope anomaly. In contrast, given reducing conditions, two isotopically distinct sulfur species such as elemental sulfur (polysulfur) and sulfate could be formed photochemically and precipitate at the surface, where the MIF signal could be preserved in sediment (3-5). Sulfur MIF in geological samples is regarded as indicating an anoxic atmosphere.This assertion relies on assumptions as to the origin of the MIF, although the mechanisms are still poorly known. Broad agreement in the ⌬ 36 S/⌬ 33 S ratio (ϷϪ1) in pre-2.3 Ga sedimentary rocks (1, 6, 7) and those produced in the laboratory by SO 2 photolysis suggest that photodissociation of gas-phase SO 2 most likely accounts for MIF in the Archean (2). Indeed, SO 2 photolysis is a key rate limiting step, particularly in a low-O 2 reducing atmosphere (4, 8). In addition, two mechanisms have been proposed whereby sulfur MIF could be formed under oxidizing conditions in the modern atmosphere: (i) Photolysis of SO 3 at altitudes greater than Ϸ50 km, where reaction between SO 3 and H 2 O is slow, is claimed to be responsible for the MIF found in modern stratospheric aerosol (8). In contrast, at lower altitudes, SO from SO 2 photolysis reforms SO 2 , so fractionation in SO 2 photolysis would not affect the isotopic compos...

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Carbonyl sulfide isotopologues: Ultraviolet absorption cross sections and stratospheric photolysis

Cited by 25 publications

References 38 publications

The ultraviolet spectrum of OCS from first principles: Electronic transitions, vibrational structure and temperature dependence

The ultraviolet spectrum of OCS from first principles: Electronic transitions, vibrational structure and temperature dependence

OCS photolytic isotope effects from first principles: sulfur and carbon isotopes, temperature dependence and implications for the stratosphere

Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox

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