Kinetics of the reactions of CH2Br and CH2I radicals with molecular oxygen at atmospheric temperatures

Eskola, Arkke J.; Wójcik-Pastuszka, Dorota; Ratajczak, Emil; Timonen, Raimo S.

doi:10.1039/b516291b

Cited by 80 publications

(153 citation statements)

References 45 publications

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“…The flow reactor with laser photolysis coupled to the resonance gas lamp photoionization mass spectrometer (LP-RPIMS) used in this work has been described previously, 15,16 and only a brief 10 The main photolysis channel leads to C3−C4 bond fission, but in addition other products are formed:…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Gas Phase Kinetics and Equilibrium of Allyl Radical Reactions with NO and NO₂

et al. 2013

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Allyl radical reactions with NO and NO 2 were studied in direct, time-resolved experiments in a temperature controlled tubular flow reactor connected to a laser photolysis/photoionization mass spectrometer (LP-PIMS). In the C 3 H 5 + NO reaction 1, a dependence on the bath gas density was observed in the determined rate coefficients and pressure falloff parametrizations were performed. The obtained rate coefficients vary between 0.30− 14.2 × 10 −12 cm 3 s −1 (T = 188−363 K, p = 0.39−23.78 Torr He) and possess a negative temperature dependence. The rate coefficients of the C 3 H 5 + NO 2 reaction 2 did not show a dependence on the bath gas density in the range used (p = 0.47−3.38 Torr, T = 201−363 K), and they can be expressed as a function of temperature with k(C 3 H 5 + NO 2 ) = (3.97 ± 0.84) × 10 −11 × (T/300 K) −1.55±0.05 cm 3 s −1 . In the C 3 H 5 + NO reaction, above 410 K the observed C 3 H 5 radical signal did not decay to the signal background, indicating equilibrium between C 3 H 5 + NO and C 3 H 5 NO. This allowed the C 3 H 5 + NO ⇄ C 3 H 5 NO equilibrium to be studied and the equilibrium constants of the reaction between 414 and 500 K to be determined. With the standard second-and third-law analysis, the enthalpy and entropy of the C 3 H 5 + NO ⇄ C 3 H 5 NO reaction were obtained. Combined with the calculated standard entropy of reaction (ΔS°2 98 = 137.2 J mol −1 K −1 ), the third-law analysis resulted in ΔH°2 98 = 102.4 ± 3.2 kJ mol −1 for the C 3 H 5 −NO bond dissociation enthalpy. ■ INTRODUCTIONReactive hydrocarbon free radicals and nitrogen oxides (NO x = NO + NO 2 ) are produced in several common environments. Energy released by burning of hydrocarbons creates a variety of reactive intermediates, including unsaturated alkenyl radicals, and combustion under atmospheric conditions leads to the formation of nitrogen oxides. 1,2 Oxides of nitrogen are primary anthropogenic pollutants but also have natural sources in the atmosphere. 3,4 The principles governing mutual reactions of alkenyl radicals and NO x are important for the understanding of hydrocarbon oxidation mechanisms and optimization of combustion processes.Allyl radical (C 3 H 5 ) is the simplest conjugated, resonancestabilized alkenyl radical. Alkenyl radicals are formed in hydrogen abstraction reactions by reactive species (e.g., OH or other radicals) from carbon atoms at the β-position to the double bond in alkenes and by pyrolysis of larger hydrocarbons at elevated temperatures. 5−7 Small unsaturated hydrocarbon radicals with resonance-stabilized structures are thermodynamically more stable than similar saturated radicals lacking resonance stabilization. Consequently, they reach higher concentrations under combustion conditions and play a role in the molecular weight growth chemistry. They are identified as precursors for polycyclic aromatic hydrocarbons (PAHs) and, subsequently, for soot formation. 8−10 In the present work, two reactions of allyl radical with nitrogen oxides were investigated:(1)Both reactions have been stu...

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Section: ■ Experimental Sectionmentioning

confidence: 99%

Gas Phase Kinetics and Equilibrium of Allyl Radical Reactions with NO and NO₂

et al. 2013

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“…2,3 Haloalkyl fragments also play a role in atmospheric chemistry as they are generally thought to form peroxy radicals after reacting with O2. 37 As with the CH2I radical, reaction of the CHICl radical with O2 appears to forms a carbonyl oxide or Criegee intermediate in comparably high yield. Pressuredependent measurements of the CH2I + O2 reaction indicate a CH2OO yield of 77% at 15 Torr (the pressure used in the measurement of the ClCHOO absorption cross section), decreasing to around 30% at atmospheric pressure.…”

Section: Atmospheric Implicationsmentioning

confidence: 99%

“…[31][32][33][34][35] Photolysis of CH2I2 in the presence of O2 was first demonstrated by Welz et al 36 to be an efficient route to generate CH2OO in sufficient concentration for kinetics studies at low pressure, following initial work by Eskola et al who had identified I atom formation in the CH2I + O2 reaction. 37 The CH2OO yield in the CH2I + O2 reaction approaches unity at low pressure, decreasing to ~30% at atmospheric pressure. [38][39][40] The UV absorption spectrum of CH2OO has been measured using several spectroscopic techniques.…”

mentioning

confidence: 99%

UV photodissociation dynamics of CHI₂Cl and its role as a photolytic precursor for a chlorinated Criegee intermediate

Kapnas

Toulson

Foreman

et al. 2017

Phys. Chem. Chem. Phys.

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Photolysis of geminal diiodoalkanes in the presence of molecular oxygen has become an established route to the laboratory production of several Criegee intermediates, and such compounds also have marine sources. Here, we explore the role that the trihaloalkane, chlorodiiodomethane (CHI2Cl), may play as a photolytic precursor for the chlorinated Criegee intermediate ClCHOO. CHI2Cl has been synthesized and its UV absorption spectrum measured; relative to that of CH2I2 the spectrum is shifted to longer wavelength and the photolysis lifetime is calculated to be less than two minutes.The photodissociation dynamics have been investigated using DC slice imaging, probing ground state I and spin-orbit excited I* atoms with 2+1 REMPI and single-photon VUV ionization. Total translational energy distributions are bimodal for I atoms and unimodal for I*, with around 72% of the available energy partitioned in to the internal degrees of freedom of the CHICl radical product, independent of photolysis wavelength. A bond dissociation energy of D0 = 1.73±0.11 eV is inferred from the wavelength dependence of the translational energy release, which is slightly weaker than typical C-I bonds. Analysis of the photofragment angular distributions indicate dissociation is prompt and occurs primarily via transitions to states of A″ symmetry. Complementary high-level MRCI calculations, including spin-orbit coupling, have been performed to characterize the excited states and confirm that states of A″ symmetry with highly mixed singlet and triplet character are predominantly responsible for the absorption spectrum. Transient absorption spectroscopy has been used to measure the absorption spectrum of ClCHOO produced from the reaction of CHICl with O2 over the range 345-440 nm. The absorption spectrum, tentatively assigned to the syn conformer, is at shorter wavelengths relative to that of CH2OO and shows far weaker vibrational structure.3

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“…Sunlight can efficiently induce the photolytic decomposition of CH 2 I 2 to form CH 2 I + I; the reaction of CH 2 I + O 2 eventually releases a second I atom; these I atoms might destroy ozone or become transformed to aerosol. 58,59 Even though the reaction of CH 2 I + O 2 has been investigated extensively, [52][53][54][55][56][60][61][62][63][64][65][66] a detailed mechanism of this reaction was established only recently. 67 The proposed mechanisms in the early studies were incomplete because only product channels for the formation of ICH 2 OO and H 2 CO + IO, not CH 2 OO + I, were considered.…”

Section: A Ch 2 I + Omentioning

confidence: 99%

Perspective: Spectroscopy and kinetics of small gaseous Criegee intermediates

Lee

2015

The Journal of Chemical Physics

159

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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Kinetics of the reactions of CH2Br and CH2I radicals with molecular oxygen at atmospheric temperatures

Cited by 80 publications

References 45 publications

Gas Phase Kinetics and Equilibrium of Allyl Radical Reactions with NO and NO₂

Gas Phase Kinetics and Equilibrium of Allyl Radical Reactions with NO and NO₂

UV photodissociation dynamics of CHI₂Cl and its role as a photolytic precursor for a chlorinated Criegee intermediate

Perspective: Spectroscopy and kinetics of small gaseous Criegee intermediates

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Kinetics of the reactions of CH2Br and CH2I radicals with molecular oxygen at atmospheric temperatures

Cited by 80 publications

References 45 publications

Gas Phase Kinetics and Equilibrium of Allyl Radical Reactions with NO and NO2

Gas Phase Kinetics and Equilibrium of Allyl Radical Reactions with NO and NO2

UV photodissociation dynamics of CHI2Cl and its role as a photolytic precursor for a chlorinated Criegee intermediate

Perspective: Spectroscopy and kinetics of small gaseous Criegee intermediates

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Product

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Gas Phase Kinetics and Equilibrium of Allyl Radical Reactions with NO and NO₂

Gas Phase Kinetics and Equilibrium of Allyl Radical Reactions with NO and NO₂

UV photodissociation dynamics of CHI₂Cl and its role as a photolytic precursor for a chlorinated Criegee intermediate