Comparison of rovibronic density of asymmetric versus symmetric NO2 isotopologues at dissociation threshold: Broken symmetry effects

Jost, R.; Michalski, Greg; Thiemens, M. H.

doi:10.1063/1.1978873

Cited by 6 publications

(8 citation statements)

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“…Recent work by Marcus and coworkers (26)(27)(28) is perhaps the most thorough treatment, and they have suggested that nonstatistical RRKM effects arise because of differences in the rovibronic coupling efficiency of the asymmetric molecule when compared with the symmetric isomer. Recent NO 2 spectroscopic data appear to bear the theory out (29), but the uncertainties in that study remain significant, and no mass spectrometer isotope data on the unimolecular decay of NO 2 are available. Because the basis of the ozone MIF theory is symmetry driven, it is implied that the anomalous enrichment must be contained in the terminal atoms of ozone.…”

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confidence: 99%

The role of symmetry in the mass independent isotope effect in ozone

Michalski

Bhattacharya

2009

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

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Understanding the internal distribution of ''anomalous'' isotope enrichments has important implications for validating theoretical postulates on the origin of these enrichments in molecules such as ozone and for understanding the transfer of these enrichments to other compounds in the atmosphere via mass transfer. Here, we present an approach, using the reaction NO 2 ؊ ؉ O3, for assessing the internal distribution of the (7) and non-mass-dependent (NOMAD) (8, 9).The most thoroughly studied MIF system is that of ozone formation. Ozone generated by electric discharge or UV photolysis can produce ⌬ 17 O values of 30-40‰ (‰ ϭ parts per thousand). There have also been numerous studies that have experimentally quantified the pressure and temperature dependence of the isotopic enrichments (10, 11). Most recently, the transfer of the ⌬ 17 O anomaly from ozone to other compounds during oxidation reactions (via atom transfer, e.g., mass balance) has been used to elucidate chemical oxidation pathways in modern atmospheres (16-21). These include ⌬ 17 O observations in atmospheric nitrate, sulfate, CO 2 , and N 2 O. ⌬ 17 O variations in atmospheric nitrate and sulfate are intriguing because they have opened the possibility of using these ⌬ 17 O variations in ice cores as a proxy for paleo-oxidation chemistry (22,23). Modeling such transfer reactions, however, requires knowledge of the internal distribution of the ⌬ 17 O anomaly, i.e., how much is contained in the central versus terminal atoms of ozone, because many atmospheric oxidations are thought to occur through terminal-only transition states.Theories as to the origin of the MIF effect have taken many turns (7,8,24,25), and some theories seem more adept at handling specific experimental cases than others. Most have symmetry as the main, albeit ad hoc, causal mechanism for producing MIF. Recent work by Marcus and coworkers (26-28) is perhaps the most thorough treatment, and they have suggested that nonstatistical RRKM effects arise because of differences in the rovibronic coupling efficiency of the asymmetric molecule when compared with the symmetric isomer. Recent NO 2 spectroscopic data appear to bear the theory out (29), but the uncertainties in that study remain significant, and no mass spectrometer isotope data on the unimolecular decay of NO 2 are available. Because the basis of the ozone MIF theory is symmetry driven, it is implied that the anomalous enrichment must be contained in the terminal atoms of ozone. To be clear, there maybe overall isotopic enrichment (␦ 18 O, ␦ 17 O) distributed throughout the molecule based on isotopologue zero-point energy differences (30), but the 17 O excess (⌬ 17 O) is expected to be only in the terminal position. Others, however, have argued against the symmetry theory (31-33) and have placed anomalous enrichments, even negative ⌬ 17 O values (34), throughout ozone in an attempt to reconcile experimental observations. Precise and accurate measurements of ozone's ⌬ 17 O internal distribution is therefore needed to test the symmet...

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confidence: 99%

The role of symmetry in the mass independent isotope effect in ozone

Michalski

Bhattacharya

2009

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

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“…The composition of organics from Murchison (16) is also shown and may be explained by a combination of fractionation at different wavelengths. The mass-independent isotopic fractionation during VUV photodissociation has been measured and theoretically calculated for triatomic molecules, such as CO 2 , NO 2 , N 2 O, and SO 2 (27,29,(46)(47)(48)(49)(50)(51)(52)(53). There is no common physical chemical mechanism for these anomalous processes, and several molecule-specific mechanisms have been proposed.…”

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confidence: 99%

Sulfur isotopic fractionation in vacuum UV photodissociation of hydrogen sulfide and its potential relevance to meteorite analysis

Chakraborty

Jackson

Ahmed

et al. 2013

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

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Select meteoritic classes possess mass-independent sulfur isotopic compositions in sulfide and organic phases. Photochemistry in the solar nebula has been attributed as a source of these anomalies. Hydrogen sulfide (H 2 S) is the most abundant gas-phase species in the solar nebula, and hence, photodissociation of H 2 S by solar vacuum UV (VUV) photons (especially by Lyman-α radiation) is a relevant process. Because of experimental difficulties associated with accessing VUV radiation, there is a paucity of data and a lack of theoretical basis to test the hypothesis of a photochemical origin of mass-independent sulfur. Here, we present multiisotopic measurements of elemental sulfur produced during the VUV photolysis of H 2 S. Mass-independent sulfur isotopic compositions are observed. The observed isotopic fractionation patterns are wavelengthdependent. VUV photodissociation of H 2 S takes place through several predissociative channels, and the measured mass-independent fractionation is most likely a manifestation of these processes. Meteorite sulfur data are discussed in light of the present experiments, and suggestions are made to guide future experiments and models.chondrites | achondrites | isotope

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“…In recent years several spectroscopic studies have focused on the complexity of the A 2 B 2 -X 2 A 1 electronic spectrum of nitrogen-dioxide, NO 2 [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. This spectrum is very dense and vibronically highly irregular as a consequence of a strong vibronic coupling between the X 2 A 1 ground state and the lowest electronically excited A 2 B 2 state via the asymmetric stretch coordinate of b 2 symmetry.…”

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confidence: 98%

“…NO 2 [1] about 30 K = 1 sub-bands on a total of 250 bands were identified. In the present case substantially less and mainly16 O 14 N 16 O transitions are unambiguously identified as originating from K = 1.…”

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confidence: 99%