Early time detection of OH radical products from energized Criegee intermediates CH2OO and CH3CHOO

Lu, Lu; Beames, Joseph M.; Lester, Marsha I.

doi:10.1016/j.cplett.2014.02.049

Cited by 24 publications

(20 citation statements)

References 34 publications

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“…The photolytically generated CH 2 I radicals react with O 2 to form highly internally excited CH 2 OO. 18,33 The CH 2 OO is collisionally stabilized in the capillary tube and cooled in the ensuing supersonic expansion.…”

Section: Experimental Methodsmentioning

confidence: 99%

Velocity map imaging of O-atom products from UV photodissociation of the CH2OO Criegee intermediate

Fang

Beames

et al. 2015

The Journal of Chemical Physics

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UV excitation of jet-cooled CH2OO X(1)A' to the excited B(1)A' electronic states results in dissociation to two spin-allowed product channels: H2CO X(1)A1 + O (1)D and H2CO a(3)A″ + O (3)P. In this study, the higher energy H2CO a(3)A″ + O (3)P channel is characterized by velocity map imaging and UV action spectroscopy, in both cases utilizing 2 + 1 resonance enhanced multiphoton ionization detection of O (3)P products, which complements a prior experimental study on the lower energy H2CO X(1)A1 + O (1)D channel [Lehman et al., J. Chem. Phys. 139, 141103 (2013)]. Anisotropic angular distributions indicative of rapid dissociation are obtained at 330 and 350 nm, along with broad and unstructured total kinetic energy distributions that provide insight into the internal excitation of the H2CO a(3)A″ co-fragment. A harmonic normal mode analysis points to significant vibrational excitation of the CH2 wag and C-O stretch modes of the H2CO a(3)A″ fragment upon dissociation. At each UV wavelength, the termination of the kinetic energy distribution reveals the energetic threshold for the H2CO a(3)A″ + O (3)P product channel of ca. 76 kcal mol(-1) (378 nm) and also establishes the dissociation energy from CH2OO X(1)A' to H2CO X(1)A1 + O(1)D products of D0 ≤ 49.0 ± 0.3 kcal mol(-1), which is in accord with prior theoretical studies. The threshold for the H2CO a(3)A″ + O (3)P channel is also evident as a more rapid falloff on the long wavelength side of the O (3)P action spectrum as compared to the previously reported UV absorption spectrum for jet-cooled CH2OO [Beames et al., J. Am. Chem. Soc. 134, 20045 (2012)]. Modeling suggests that the O (3)P yield increases uniformly from 378 to 300 nm.

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Section: Experimental Methodsmentioning

confidence: 99%

Velocity map imaging of O-atom products from UV photodissociation of the CH2OO Criegee intermediate

Fang

Beames

et al. 2015

The Journal of Chemical Physics

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“…In the first paper [59] the photolysis that creates iodoalkyl radicals occurs 1 mm after expansion of the gas mixture into vacuum, in the dense region of the jet with molecular collisions. In both cases they form CIs using iodoalkyl radicals + O 2 in a pulsed molecular beam valve, but with an important difference for the method of CI excitation.…”

Section: International Reviews In Physical Chemistry 335mentioning

confidence: 99%

“…In the chemically activated study [59], the authors measure rotational and translational energy distributions of OH by measuring the intensity of Doppler-broadened transitions in the OH A( 2 Σ + ) ← X( 2 Π) (1,0) P 1 branch. For CH 2 OO production, the CH 2 I radical precursor is expected to have a bimodal distribution of internal energy, peaked at 36 and 54 kcal mol −1 , corresponding to its I( 2 P 1/2 ) and I( 2 P 3/2 ) cofragment [61].…”

Section: International Reviews In Physical Chemistry 335mentioning

confidence: 99%

The physical chemistry of Criegee intermediates in the gas phase

Osborn

Taatjes

2015

International Reviews in Physical Chemistry

240

207

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Carbonyl oxides, also known as Criegee intermediates, are key intermediates in both gas phase ozonolysis of unsaturated hydrocarbons in the troposphere and solution phase organic synthesis via ozonolysis. Although the study of Criegee intermediates in both arenas has a long history, direct studies in the gas phase have only recently become possible through new methods of generating stabilised Criegee intermediates in sufficient quantities. This advance has catalysed a large number of new experimental and theoretical investigations of Criegee intermediate chemistry. In this article we review the physical chemistry of Criegee intermediates, focusing on their molecular structure, spectroscopy, unimolecular and bimolecular reactions. These recent results have overturned conclusions from some previous studies, while confirming others, and have clarified areas of investigation that will be critical targets for future studies. In addition to expanding our fundamental understanding of Criegee intermediates, the rapidly expanding knowledge base will support increasingly predictive models of their impacts on society.

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“…30,55,63,65,74 At a pressure less than 40 Torr, unresolved spectra of internally excited CO and CO 2 , presumably produced from decomposition of CH 2 OO after isomerization, were observed with a step-scan FTIR spectrometer. 67 One important product is OH, which has also been observed in the reactions of ozone and alkenes.…”

Section: Identification Of Other Productsmentioning

confidence: 99%

“…75 The OH radical from the unimolecular decay of energetic CH 2 OO was detected with laser-induced fluorescence shortly after its formation in a capillary on a pulsed nozzle upon photolysis of CH 2 I 2 precursors at 248 nm and subsequent reaction with O 2 . 74 From the Doppler width, the OH radicals were produced with average rotational energies of 4-8 kJ mol…”

Section: Identification Of Other Productsmentioning

confidence: 99%

Perspective: Spectroscopy and kinetics of small gaseous Criegee intermediates

Lee

2015

The Journal of Chemical Physics

158

122

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The Criegee intermediates, carbonyl oxides proposed by Criegee in 1949 as key intermediates in the ozonolysis of alkenes, play important roles in many aspects of atmospheric chemistry. Because direct detection of these gaseous intermediates was unavailable until recently, previous understanding of their reactions, derived from indirect experimental evidence, had great uncertainties. Recent laboratory detection of the simplest Criegee intermediate CH2OO and some larger members, produced from ultraviolet irradiation of corresponding diiodoalkanes in O2, with various methods such as photoionization, ultraviolet absorption, infrared absorption, and microwave spectroscopy opens a new door to improved understanding of the roles of these Criegee intermediates. Their structures and spectral parameters have been characterized; their significant zwitterionic nature is hence confirmed. CH2OO, along with other products, has also been detected directly with microwave spectroscopy in gaseous ozonolysis reactions of ethene. The detailed kinetics of the source reaction, CH2I + O2, which is critical to laboratory studies of CH2OO, are now understood satisfactorily. The kinetic investigations using direct detection identified some important atmospheric reactions, including reactions with NO2, SO2, water dimer, carboxylic acids, and carbonyl compounds. Efforts toward the characterization of larger Criegee intermediates and the investigation of related reactions are in progress. Some reactions of CH3CHOO are found to depend on conformation. This perspective examines progress toward the direct spectral characterization of Criegee intermediates and investigations of the associated reaction kinetics, and indicates some unresolved problems and prospective challenges for this exciting field of research.

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Early time detection of OH radical products from energized Criegee intermediates CH2OO and CH3CHOO

Cited by 24 publications

References 34 publications

Velocity map imaging of O-atom products from UV photodissociation of the CH2OO Criegee intermediate

Velocity map imaging of O-atom products from UV photodissociation of the CH2OO Criegee intermediate

The physical chemistry of Criegee intermediates in the gas phase

Perspective: Spectroscopy and kinetics of small gaseous Criegee intermediates

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