CH<sub>3</sub>OCI: UV/visible absorption cross sections, J values and atmospheric significance

Crowley, John N.; Helleis, Frank; Müller, Rolf; Moortgat, G. K.; Crutzen, Paul J.

doi:10.1029/94jd01829

Cited by 35 publications

(46 citation statements)

References 26 publications

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“…Recent calculations on methylhypochlorite CH 3 OCl and chloromethanol ClCH 2 OH (11, 12) using this ccp-VDZ + sp basis set have been very successful. The values obtained are in reasonable agreement with the results both of more extensive computations (9) and of experimental findings (6)(7)(8).…”

Section: Choh To Its Electronic Excited States and Comparison Betweensupporting

confidence: 91%

“…In addition to the well-known reaction channel leading to the formation of CH 3 O and ClOO Helleis et al (5) found a second reaction channel forming methylhypochlorite CH 3 OCl. The electronic spectrum and possible photofragmentation processes of CH 3 OCl are subject of many recent experimental (6)(7)(8) and theoretical studies (9,10). The corresponding authors generally conclude that chlorine-substituted hydrocarbons play an important role in atmospheric chemistry as a possible chlorine reservoir.…”

Section: Introductionmentioning

confidence: 99%

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Ab Initio MRD-CI Investigation of the Electronic Spectrum of Dichloromethanol Cl2CHOH

Schnell

Mühlhäuser

Peyerimhoff

2002

Journal of Molecular Spectroscopy

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Section: Choh To Its Electronic Excited States and Comparison Betweensupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Ab Initio MRD-CI Investigation of the Electronic Spectrum of Dichloromethanol Cl2CHOH

Schnell

Mühlhäuser

Peyerimhoff

2002

Journal of Molecular Spectroscopy

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“…The dominant source of HO x radicals under the conditions of the polar lower stratosphere in late winter and early spring is not the production of O( 1 D) radicals through ozone photolysis with subsequent reaction with H 2 O, but rather the radical channel of the photolysis of CH 2 O (Reaction R14) Crowley et al, 1994). Thus, the photolysis of CH 2 O (radical channel) is effectively driving the depletion of HCl.…”

Section: The Path To Full Activation Of Hclmentioning

confidence: 99%

The maintenance of elevated active chlorine levels in the Antarctic lower stratosphere through HCl null cycles

Müller¹,

Grooß²,

Zafar

et al. 2018

Atmos. Chem. Phys.

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Abstract. The Antarctic ozone hole arises from ozone destruction driven by elevated levels of ozone destroying ("active") chlorine in Antarctic spring. These elevated levels of active chlorine have to be formed first and then maintained throughout the period of ozone destruction. It is a matter of debate how this maintenance of active chlorine is brought about in Antarctic spring, when the rate of formation of HCl (considered to be the main chlorine deactivation mechanism in Antarctica) is extremely high. Here we show that in the heart of the ozone hole (16-18 km or 85-55 hPa, in the core of the vortex), high levels of active chlorine are maintained by effective chemical cycles (referred to as HCl null cycles hereafter). In these cycles, the formation of HCl is balanced by immediate reactivation, i.e. by immediate reformation of active chlorine. Under these conditions, polar stratospheric clouds sequester HNO 3 and thereby cause NO 2 concentrations to be low. These HCl null cycles allow active chlorine levels to be maintained in the Antarctic lower stratosphere and thus rapid ozone destruction to occur. For the observed almost complete activation of stratospheric chlorine in the lower stratosphere, the heterogeneous reaction HCl + HOCl is essential; the production of HOCl occurs via HO 2 + ClO, with the HO 2 resulting from CH 2 O photolysis. These results are important for assessing the impact of changes of the future stratospheric composition on the recovery of the ozone hole. Our simulations indicate that, in the lower stratosphere, future increased methane concentrations will not lead to enhanced chlorine deactivation (through the reaction CH 4 + Cl −→ HCl+CH 3 ) and that extreme ozone destruction to levels below ≈ 0.1 ppm will occur until mid-century.

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“…This can be evaluated through examination of the ultraviolet (UV) absorption spectrum of CH 3 OCl. Crowley et al 12 characterized the UV absorption spectrum of gas-phase CH 3 OCl from 200 to 460 nm. A study by Jungkamp et al 13 CH 4 + Cl f CH 3 12 The absorption spectrum exhibited two peaks in the UV range, one centered at 235 nm and a weaker one peaking at 310 nm.…”

Section: Introductionmentioning

confidence: 99%

“…Crowley et al 12 characterized the UV absorption spectrum of gas-phase CH 3 OCl from 200 to 460 nm. A study by Jungkamp et al 13 CH 4 + Cl f CH 3 12 The absorption spectrum exhibited two peaks in the UV range, one centered at 235 nm and a weaker one peaking at 310 nm. Crowley et al 12 calculated a photolysis rate constant of 6.8 × 10 -5 s -1 at a pressure of 100 mbar and a zenith angle of 80°, resulting in a stratospheric lifetime for CH 3 OCl of 4.1 h. The addition of perturbed ozone conditions (i.e., gas concentrations typical of the development of an ozone hole) into this simulation was not found to alter the photolysis rate constants greatly, as the 310 nm peak was responsible for the bulk of atmospheric photodissociation.…”

Section: Introductionmentioning

confidence: 99%

Photodissociation of CH₃OCl to CH₃O + Cl at 248 nm

et al. 2004

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This study examines the 248 nm photodissociation of methyl hypochlorite (CH 3 OCl), a molecule that serves as an atmospheric chlorine reservoir. The data show that the primary photodissociation channel is cleavage of the O-Cl bond to produce Cl atoms and CH 3 O radicals, a result consistent with the direct dissociation mechanism found by other computational and experimental studies of alkyl hypohalites. Photofragment translational spectroscopy with a crossed laser-molecular beam apparatus, coupled with tunable VUV photoionization detection, identified the momentum-matched products at m/e ) 35 (Cl + from Cl atoms) and m/e ) 29 (the CHO + daughter ion of CH 3 O). Products were formed with a narrow range of recoil kinetic energies, peaking at 48 kcal/mol in the center-of-mass reference frame, with a full-width half-maximum of 4 ( 2 kcal/mol. This kinetic energy distribution shows that the CH 3 O products are formed with a very narrow range of internal energies, and a simple model shows that to conserve angular momentum this internal energy, near 20 kcal/mol, is partitioned primarily to rotational energy. Thus CH 3 OCl could serve as a photolytic precursor of CH 3 O radicals with high and well-defined rotational and translational energies.

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CH₃OCI: UV/visible absorption cross sections, J values and atmospheric significance

Cited by 35 publications

References 26 publications

Ab Initio MRD-CI Investigation of the Electronic Spectrum of Dichloromethanol Cl2CHOH

Ab Initio MRD-CI Investigation of the Electronic Spectrum of Dichloromethanol Cl2CHOH

The maintenance of elevated active chlorine levels in the Antarctic lower stratosphere through HCl null cycles

Photodissociation of CH₃OCl to CH₃O + Cl at 248 nm

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CH3OCI: UV/visible absorption cross sections, J values and atmospheric significance

Cited by 35 publications

References 26 publications

Ab Initio MRD-CI Investigation of the Electronic Spectrum of Dichloromethanol Cl2CHOH

Ab Initio MRD-CI Investigation of the Electronic Spectrum of Dichloromethanol Cl2CHOH

The maintenance of elevated active chlorine levels in the Antarctic lower stratosphere through HCl null cycles

Photodissociation of CH3OCl to CH3O + Cl at 248 nm

Contact Info

Product

Resources

About

CH₃OCI: UV/visible absorption cross sections, J values and atmospheric significance

Photodissociation of CH₃OCl to CH₃O + Cl at 248 nm