Reaction Of CH2OO Research Articles

Direct experimental probing and theoretical analysis of the reaction between the simplest Criegee intermediate CH2OO and isoprene.

Recent advances in the spectroscopy of Criegee intermediates (CI) have enabled direct kinetic studies of these highly reactive chemical species. The impact of CI chemistry is currently being incorporated into atmospheric models, including their reactions with trace organic and inorganic compounds. Isoprene, C5H8, is a doubly-unsaturated hydrocarbon that accounts for the largest share of all biogenic emissions around the globe and is also a building block of larger volatile organic compounds. We report direct measurements of the reaction of the simplest CI (CH2OO) with isoprene, using time-resolved cavity-enhanced UV absorption spectroscopy. We find the reaction to be pressure-independent between 15-100 Torr, with a rate coefficient that varies from (1.5 ± 0.1) × 10-15 cm3 molecule-1 s-1 at room temperature to (23 ± 2) × 10-15 cm3 molecule-1 s-1 at 540 K. Quantum chemical and transition-state theory calculations of 16 unique channels for CH2OO + isoprene somewhat underpredict the observed T-dependence of the total reaction rate coefficient, but are overall in good agreement with the experimental measurements. This reaction is broadly similar to those with smaller alkenes, proceeding by 1,3-dipolar cycloaddition to one of the two conjugated double bonds of isoprene.

Role of water clusters in the reaction of the simplest Criegee intermediate CH2OO with water vapour

A comprehensive theoretical study on the role of water clusters ((H2O) n , n = 3–5) in the reaction of CH2OO with water vapour is done at the CCSD(T)//M06-2X/6-311 + G(2df,2p) level of theory. Our simulation results show that the contribution of entropic effect is significantly increased with the increase in the number of water molecules involved. The main products of CH2OO reaction with water vapour are α-hydroxymethyl hydroperoxide and its isomers. Contrary to the reaction of CH2OO with unimolecular water (10.91 kcal mol−1), the barriers of reactions with bi- and trimolecular water are further reduced to 5.25 and 4.75 kcal mol−1, respectively. Among these three reactions, the predominant pathway is the reaction of CH2OO with bimolecular water owing to its lower barrier and the high concentration of (H2O)2 ([(H2O)2] ≈ 2.47 × 1014 molecules cm−3). The presence of water clusters exhibits a dramatic catalytic effect in the CH2OO reaction with bimolecular water as it lowers the energy barrier by 4.0 kcal mol−1. The relative reaction rates, which are determined at temperatures from 273 to 323 K and 85 % relative humidity, reveal that the most favourable pathway for the atmospheric removal of CH2OO is indeed via its reaction with bimolecular water.

New Mechanistic Pathways for Criegee-Water Chemistry at the Air/Water Interface.

Understanding Criegee chemistry has become one of central topics in atmospheric research recently. The reaction of Criegee intermediates with gas-phase water clusters has been widely viewed as a key Criegee reaction in the troposphere. However, the effect of aerosols or clouds on Criegee chemistry has received little attention. In this work, we have investigated the reaction between the smallest Criegee intermediate, CH2OO, and water clusters in the gas phase, as well as at the air/water surface using ab initio quantum chemical calculations and adaptive buffered force quantum mechanics/molecular mechanics (QM/MM) dynamics simulations. Our simulation results show that the typical time scale for the reaction of CH2OO with water at the air/water interface is on the order of a few picoseconds, 2-3 orders of magnitude shorter than that in the gas phase. Importantly, the adbf-QM/MM dynamics simulations suggest several reaction pathways for the CH2OO + water reaction at the air/water interface, including the loop-structure-mediated mechanism and the stepwise mechanism. Contrary to the conventional gas-phase CH2OO reaction, the loop-structure is not a prerequisite for the stepwise mechanism. For the latter, a water molecule and the CH2OO at the air/water interface, upon their interaction, can result in the formation of (H3O)(+) and (OH)CH2(OO)(-). Thereafter, a hydrogen bond can be formed between (H3O)(+) and the terminal oxygen atom of (OH)CH2(OO)(-), leading to direct proton transfer and the formation of α-hydroxy methylperoxide, HOCH2OOH. The mechanistic insights obtained from this simulation study should motivate future experimental studies of the effect of water clouds on Criegee chemistry.

Reactions between Criegee Intermediates and the Inorganic Acids HCl and HNO3: Kinetics and Atmospheric Implications

Criegee intermediates (CIs) are a class of reactive radicals that are thought to play a key role in atmospheric chemistry through reactions with trace species that can lead to aerosol particle formation. Recent work has suggested that water vapor is likely to be the dominant sink for some CIs, although reactions with trace species that are sufficiently rapid can be locally competitive. Herein, we use broadband transient absorption spectroscopy to measure rate constants for the reactions of the simplest CI, CH2 OO, with two inorganic acids, HCl and HNO3 , both of which are present in polluted urban atmospheres. Both reactions are fast; at 295 K, the reactions of CH2 OO with HCl and HNO3 have rate constants of 4.6×10(-11) cm(3) s(-1) and 5.4×10(-10) cm(3) s(-1) , respectively. Complementary quantum-chemical calculations show that these reactions form substituted hydroperoxides with no energy barrier. The results suggest that reactions of CIs with HNO3 in particular are likely to be competitive with those with water vapor in polluted urban areas under conditions of modest relative humidity.

Reactions between Criegee Intermediates and the Inorganic Acids HCl and HNO3: Kinetics and Atmospheric Implications

AbstractCriegee intermediates (CIs) are a class of reactive radicals that are thought to play a key role in atmospheric chemistry through reactions with trace species that can lead to aerosol particle formation. Recent work has suggested that water vapor is likely to be the dominant sink for some CIs, although reactions with trace species that are sufficiently rapid can be locally competitive. Herein, we use broadband transient absorption spectroscopy to measure rate constants for the reactions of the simplest CI, CH2OO, with two inorganic acids, HCl and HNO3, both of which are present in polluted urban atmospheres. Both reactions are fast; at 295 K, the reactions of CH2OO with HCl and HNO3 have rate constants of 4.6×10−11 cm3 s−1 and 5.4×10−10 cm3 s−1, respectively. Complementary quantum‐chemical calculations show that these reactions form substituted hydroperoxides with no energy barrier. The results suggest that reactions of CIs with HNO3 in particular are likely to be competitive with those with water vapor in polluted urban areas under conditions of modest relative humidity.

Temperature- and Pressure-Dependent Kinetics of CH2OO + CH3COCH3and CH2OO + CH3CHO: Direct Measurements and Theoretical Analysis

The rate coefficients of the gas-phase reactions CH2OO + CH3COCH3 and CH2OO + CH3CHO have been experimentally determined from 298–500 K and 4–50 Torr using pulsed laser photolysis with multiple-pass UV absorption at 375 nm, and products were detected using photoionization mass spectrometry at 10.5 eV. The CH2OO + CH3CHO reaction's rate coefficient is ∼4 times faster over the temperature 298–500 K range studied here. Both reactions have negative temperature dependence. The T dependence of both reactions was captured in simple Arrhenius expressions: k CH 2 OO + CH 3 COCH 3(T)=7±2.5×10−15 cm 3 molecule −1s−1exp[+9.3±2.9 kJ mol −1/RT]k CH 2 OO + CH 3 CHO (T)=3±0.8×10−14 cm 3 molecule −1s−1exp[+9.1±2.7 kJ mol −1/RT] The rate of the reactions of CH2OO with carbonyl compounds at room temperature is two orders of magnitude higher than that reported previously for the reaction with alkenes, but the A factors are of the same order of magnitude. Theoretical analysis of the entrance channel reveals that the inner 1,3-cycloaddition transition state is rate limiting at normal temperatures. Predicted rate-coefficients (RCCSD(T)-F12a/cc-pVTZ-F12//B3LYP/MG3S level of theory) in the low-pressure limit accurately reproduce the experimentally observed temperature dependence. The calculations only qualitatively reproduce the A factors and the relative reactivity between CH3CHO and CH3COCH3. The rate coefficients are weakly pressure dependent, within the uncertainties of the current measurements. The predicted major products are not detectable with our photoionization source, but heavier species yielding ions with masses m/z = 104 and 89 are observed as products from the reaction of CH2OO with CH3COCH3. The yield of m/z = 89 exhibits positive pressure dependence that appears to have already reached a high-pressure limit by 25 Torr.

Water-catalyzed decomposition of the simplest Criegee intermediate CH2OO

A comprehensive theoretical study on the gas-phase decomposition of the CH2OO intermediate is performed at the CCSD(T)//B3LYP/6-311+G(2df,2p) level in the presence of water molecules [n(H2O), n = 1–3]. The calculated results show that the most favorable route is the formation of dioxirane pathway (R3) in the unimolecular decomposition of CH2OO. For the reactions of CH2OO with uni-, bi-, and trimolecular water, the predominant pathway is the CH2OO with bimolecular water reaction as the major product is cis-HMHP. Compared with the barrier of CH2OO reaction with unimolecular water, an addition of water molecule contributes to a reduction of 4.91 kcal mol−1 for the barrier. The elimination processes of cis-HMHP have two parallel competitive pathways: trans-HCOOH + H2O (R9) and HCOH + H2O2 (R10). The apparent activation barriers of these two reactions are significantly reduced with the increase in the number of water molecules involved. The barrier of R9 is higher than that of R10 about 8–15 kcal mol−1 in the presence of water molecules, meaning that the favorable route is the formation of HCOH + H2O2 in the decomposition of cis-HMHP. The rate coefficients of CH2OO reaction with unimolecular water satisfy a positive temperature coefficient behavior at 298–500 K, whereas the rate coefficients of CH2OO reaction with bimolecular water exhibit a negative temperature dependence.

Observation of hydroxymethyl hydroperoxide in a reaction system containing CH2OO and water vapor through pure rotational spectroscopy.

Pure rotational transitions of hydroxymethyl hydroperoxide (HMHP) were observed in the discharged plasma of a CH2I2/O2/water gas mixture, where the water complex with the simplest Criegee intermediate CH2OO has been identified [M. Nakajima and Y. Endo, J. Chem. Phys. 140, 134302 (2014)]. Isotope experiments using heavy water support that the currently observed HMHP molecule was produced by the reaction of CH2OO with water vapor. The observed species was identified as the most stable conformer with the help of quantum chemical calculations. We also clarified that productions of formic acid and dioxirane are promoted by the existence of water vapor in the discharged reaction system.

A kinetic study of the CH2OO Criegee intermediate self-reaction, reaction with SO2 and unimolecular reaction using cavity ring-down spectroscopy.

Criegee intermediates are important species formed during the ozonolysis of alkenes. Reaction of stabilized Criegee intermediates with various species like SO2 and NO2 may contribute significantly to tropospheric chemistry. In the laboratory, self-reaction can be an important loss pathway for Criegee intermediates and thus needs to be characterized to obtain accurate bimolecular reaction rate coefficients. Cavity ring-down spectroscopy was used to perform kinetic measurements for various reactions of CH2OO at 293 K and under low pressure (7 to 30 Torr) conditions. For the reaction CH2OO + CH2OO (8), a rate coefficient k8 = (7.35 ± 0.63) × 10(-11) cm(3) molecule(-1) s(-1) was derived from the measured CH2OO decay rates, using an absorption cross section value reported previously. A rate coefficient of k4 = (3.80 ± 0.04) × 10(-11) cm(3) molecule(-1) s(-1) was obtained for the CH2OO + SO2 (4) reaction. An upper limit for the unimolecular CH2OO loss rate coefficient of 11.6 ± 8.0 s(-1) was deduced from studies of reaction (4). SO2 catalysed CH2OO isomerization or intersystem crossing is proposed to occur with a rate coefficient of (3.53 ± 0.32) × 10(-11) cm(3) molecule(-1) s(-1).

Kinetics of the unimolecular reaction of CH2OO and the bimolecular reactions with the water monomer, acetaldehyde and acetone under atmospheric conditions.

Stabilized Criegee Intermediates (sCIs) have been identified as oxidants of atmospheric trace gases such as SO2, NO2, carboxylic acids or carbonyls. The atmospheric sCI concentrations, and accordingly their importance for trace gas oxidation, are controlled by the rate of the most important loss processes, very likely the unimolecular reactions and the reaction with water vapour (monomer and dimer) ubiquitously present at high concentrations in the troposphere. In this study, the rate coefficients of the unimolecular reaction of the simplest sCI, formaldehyde oxide, CH2OO, and its bimolecular reaction with the water monomer have been experimentally determined at T = (297 ± 1) K and at atmospheric pressure by using a free-jet flow system. CH2OO was produced by the reaction of ozone with C2H4, and CH2OO concentrations were probed indirectly by detecting H2SO4 after titration with SO2. Time-resolved experiments yield a rate coefficient of the unimolecular reaction of k(uni) = (0.19 ± 0.07) s(-1), a value that is supported by quantum-chemical and statistical rate theory calculations as well as by additional measurements performed under CH2OO steady-state conditions. A rate coefficient of k(CH2OO+H2O) = (3.2 ± 1.2) × 10(-16) cm(3) molecule(-1) s(-1) has been determined for sufficiently low H2O concentrations (<10(15) molecule cm(-3)) that allow separation from the CH2OO reaction with the water dimer. In order to evaluate the accuracy of the experimental approach, the rate coefficients of the reactions with acetaldehyde and acetone were reinvestigated. The obtained rate coefficients k(CH2OO+acetald) = (1.7 ± 0.5) × 10(-12) and k(CH2OO+acetone) = (3.4 ± 0.9) × 10(-13) cm(3) molecule(-1) s(-1) are in good agreement with literature data.

Competing atmospheric reactions of CH2OO with SO2 and water vapour.

H2SO4 formation from the reaction CH2OO + SO2 has been measured as a function of the water vapour concentration for close to atmospheric conditions. Second-order kinetics with regard to water indicates a preferred reaction of CH2OO with the water dimer. The obtained kinetic parameters lead to the conclusion that the atmospheric fate of CH2OO is dominated by the reaction with water vapour. A comparison with results from CH3CHOO and (CH3)2COO indicates a structure dependent reactivity of stabilized Criegee intermediates.

Spectroscopy of the Simplest Criegee Intermediate CH2OO: Simulation of the First Bands in Its Electronic and Photoelectron Spectra

CH(2)OO, the simplest Criegee intermediate, and ozone are isoelectronic. They both play very important roles in atmospheric chemistry. Whilst extensive experimental studies have been made on ozone, there were no direct gas-phase studies on CH(2)OO until very recently when its photoionization spectrum was recorded and kinetics studies were made of some reactions of CH(2)OO with a number of molecules of atmospheric importance, using photoionization mass spectrometry to monitor CH(2)OO. In order to encourage more direct studies on CH(2)OO and other Criegee intermediates, the electronic and photoelectron spectra of CH(2)OO have been simulated using high level electronic structure calculations and Franck-Condon factor calculations, and the results are presented here. Adiabatic and vertical excitation energies of CH(2)OO were calculated with TDDFT, EOM-CCSD, and CASSCF methods. Also, DFT, QCISD and CASSCF calculations were performed on neutral and low-lying ionic states, with single energy calculations being carried out at higher levels to obtain more reliable ionization energies. The results show that the most intense band in the electronic spectrum of CH(2) OO corresponds to the B(1)A' ← X(1)A' absorption. It is a broad band in the region 250-450 nm showing extensive structure in vibrational modes involving O-O stretching and C-O-O bending. Evidence is presented to show that the electronic absorption spectrum of CH(2)OO has probably been recorded in earlier work, albeit at low resolution. We suggest that CH(2)OO was prepared in this earlier work from the reaction of CH(2)I with O(2) and that the assignment of the observed spectrum solely to CH(2)IOO is incorrect. The low ionization energy region of the photoelectron spectrum of CH(2)OO consists of two overlapping vibrationally structured bands corresponding to one-electron ionizations from the highest two occupied molecular orbitals of the neutral molecule. In each case, the adiabatic component is the most intense and the adiabatic ionization energies of these bands are expected to be very close, at 9.971 and 9.974 eV at the highest level of theory used.

The Ethene−Ozone Reaction in the Gas Phase

The ethene−ozone reaction was investigated in a 570 L spherical glass reactor at atmospheric pressure, using long-path FTIR spectroscopy for detection of the individual products. Experiments were performed in the presence of hydroxy and carbonyl compounds to identify the reactions of the Criegee intermediate CH2OO formed in ethene ozonolysis. Using 13C-labeled HCHO, this reaction was found to proceed via an unstable cyclic adduct which decays to the detected products HCHO, HCOOH and CO. [CH2OO + HCHO → HCHO + HCOOH (eq 13); CH2OO + HCHO → HCHO + CO + H2O (eq 14a); CH2OO + HCHO → HCHO + HCO + OH (eq 14b)] The relative rates of the reactions of CH2OO with HCOOH and HCHO were determined from the product analysis. In addition, evidence was found that the reaction of CH3CHO with the CH2OO intermediate does not exclusively produce secondary propene ozonide, but also HCHO and CO2. The results of this study have been combined with data from previous investigations to give a complete description of the gas phase o...

Production of Hydrogen Peroxide and Organic Hydroperoxides in the Reactions of Ozone with Natural Hydrocarbons in Air

Abstract Reaction of ozone with three kinds of olefins in air was studied. H2O2, CH3OOH, and HOCH2OOH were collected and analyzed with HPLC with a fluorometric detector. Direct reaction of CH2OO with H2O was found to be the source of HOCH2OOH. CH3OOH was formed only from the olefins which have a methyl group. Detailed reaction mechanisms are discussed.