Spectroscopic characterization of the complex between water and the simplest Criegee intermediate CH2OO

Reactivity and internal dynamics in the Criegee intermediate CH2OOCO2 system: A rotational study

The reaction system between the simplest Criegee intermediate, CH₂OO, and the greenhouse gas CO₂ has been investigated by Fourier transform microwave spectroscopy. The CH₂OO-CO₂ weakly bound complex was identified in the rotational spectrum, where inversion doublets due to the tunnelling motion between two equivalent configurations of the complex, with CO₂ located at one side or the other side of the CH₂OO plane, were observed. Using a two-state torsion-rotation Hamiltonian, a complete set of rotational and centrifugal distortion constants for both tunneling states were derived. In addition, the torsional energy difference between both states could be accurately determined, being 23.9687 MHz. The non-observation of the cycloaddition reaction product is in agreement with our ab initio calculations and with previous results that concluded that the reactivity of CIs toward CO₂ is measured to be quite limited.

Probing Criegee intermediate reactions with methanol by FTMW spectroscopy

Methoxymethyl hydroperoxide (HOOCH₂OCH₃) and methoxyethyl hydroperoxide (HOOC(CH₃)HOCH₃) have been characterized as the nascent reaction products from the reaction of methanol with CH₂OO and CH₃CHOO, respectively.

Observation of hydroperoxyethyl formate from the reaction between the methyl Criegee intermediate and formic acid

The hydroperoxide ester, hydroperoxyethyl formate, has been characterized as the nascent reaction product obtained from the reaction of the Criegee intermediate, CH₃CHOO, and formic acid.

Temperature-Dependent Rate Coefficient for the Reaction of CH3SH with the Simplest Criegee Intermediate

The kinetics of the reaction of the simplest Criegee intermediate CH₂OO with CH₃SH was measured with transient IR absorption spectroscopy in a temperature-controlled flow reaction cell, and the bimolecular rate coefficients were measured from 278 to 349 K and at total pressure from 10 to 300 Torr. The measured bimolecular rate coefficient at 298 K and 300 Torr is (1.01 ± 0.17)   ×  10^-12 cm³ s^-1. The results exhibit a weak negative temperature dependence: the activation energy E_a ( k = Ae^{- E_a/ RT}) is -1.83 ± 0.05 kcal mol^-1, measured at 30 and 100 Torr. Quantum chemistry calculations of the reaction rate coefficient at the QCISD(T)/CBS//B3LYP/6-311+G(2d,2p) level (1.6  ×  10^-12 cm³ s^-1 at 298 K; E_a = - 2.80 kcal mol^-1) are in reasonable agreement with the experimental results. The experimental and theoretical results of the reaction of CH₂OO with CH₃SH are compared to the reactions of CH₂OO with methanol and hydrogen sulfide, and the trends in reactivity are discussed. The results of the present work indicate that this reaction has a negligible influence to atmospheric CH₂OO or CH₃SH.

The reactivity of the Criegee intermediate CH3CHOO with water probed by FTMW spectroscopy

The reaction of Criegee intermediates with water is one of the dominant removal mechanisms for these species in the atmosphere. The reactivity of alkyl substituted Criegee intermediates has been shown to be affected by the nature and location of the substituents. CH₃CHOO, acetaldehyde oxide, can be considered as a prototypical Criegee intermediate with a single alkyl substituent to examine the conformer specific reactivity for Criegee intermediates. Pulsed Fourier-transform microwave spectroscopy has been used to probe the products resulting from the reaction between CH₃CHOO and water. The hydrogen-bonded complex between CH₃CHOO and water together with the reaction product, hydroxyethyl hydroperoxide, were observed in the discharged plasma of a CH₃CHI₂/O₂/water gas mixture. The experimentally determined rotational parameters support the identification of the complex between water and the syn-CH₃CHOO conformer and two conformers of hydroxyethyl hydroperoxide, produced from the anti-CH₃CHOO conformer and water.

Structure-dependent reactivity of Criegee intermediates studied with spectroscopic methods

Criegee intermediates are very reactive carbonyl oxides that are formed in reactions of unsaturated hydrocarbons with ozone (ozonolysis). Recently, Criegee intermediates have gained significant attention since a new preparation method has been reported in 2012, which employs the reaction of iodoalkyl radical with molecular oxygen: for instance, CH₂I + O₂ → CH₂OO + I. This new synthesis route can produce Criegee intermediates with a high number density, which allows direct detection of the Criegee intermediate via various spectroscopic tools, including vacuum UV photoionization mass spectrometry, absorption and action spectroscopy in the UV and IR regions, and microwave spectroscopy. Criegee intermediates have been thought to play important roles in atmospheric chemistry, such as in OH radical formation as well as oxidation of atmospheric gases such as SO₂, NO₂, volatile organic compounds, organic and inorganic acids, and even water. These reactions are relevant to acid rain and aerosol formation. Kinetics data including rate coefficients, product yields and their temperature and pressure dependences are important for understanding and modeling relevant atmospheric chemistry. In fundamental physical chemistry, Criegee intermediates have unique and interesting features, which have been partially revealed through spectroscopic, kinetic, and dynamic investigations. Although previous review articles have discussed Criegee intermediates, new data and knowledge on Criegee intermediates are still being accumulated. In this tutorial review, we have focused on structure-dependent reactivity of Criegee intermediates and various spectroscopic tools that have been utilized to probe the kinetics of Criegee intermediates.

The reaction between the methyl Criegee intermediate and hydrogen chloride: an FTMW spectroscopic study

Reaction of methyl substituted Criegee intermediate, CH₃CHOO, with hydrogen chloride investigated by rotational spectroscopy.

Fourier-transform microwave spectroscopy of a halogen substituted Criegee intermediate ClCHOO

Pure rotational spectra of the chloro-substituted Criegee intermediate (ClCHOO) were observed by Fourier-transform microwave spectroscopy. Two conformers (syn and anti) of the isolated molecule were identified from the rotational spectra of the parent and ³⁷Cl and ¹³C isotopologues detected in natural abundance. Rotational constants, centrifugal distortion constants, and all components of the nuclear quadrupole coupling tensor were determined for both conformers. Structural features of the molecule have been rationalized with supporting ab initio calculations and the natural bond orbital analysis, which suggest that the conformational preferences are driven by hyperconjugative effects.

Hydration of the simplest α-keto acid: a rotational spectroscopic and ab initio study of the pyruvic acid–water complex

Non-covalent interactions analysis of hydrogen bonding in the pyruvic acid water complex.

A kinetic study of the CH2OO Criegee intermediate reaction with SO2, (H2O)2, CH2I2 and I atoms using OH laser induced fluorescence

The OH laser induced fluorescence method was used to study the kinetics of CH₂OO reacting with SO₂, (H₂O)₂, CH₂I₂ and I atoms.

Atmospheric Chemistry of Criegee Intermediates: Unimolecular Reactions and Reactions with Water

Criegee intermediates are produced in the ozonolysis of unsaturated hydrocarbons in the troposphere, and understanding their fate is a prerequisite to modeling climate-controlling atmospheric aerosol formation. Although some experimental and theoretical rate data are available, they are incomplete and partially inconsistent, and they do not cover the tropospheric temperature range. Here, we report quantum chemical rate constants for the reactions of stabilized formaldehyde oxide (CH₂OO) and acetaldehyde oxide (syn-CH₃CHOO and anti-CH₃CHOO) with H₂O and for their unimolecular reactions. Our results are obtained by combining post-CCSD(T) electronic structure benchmarks, validated density functional theory potential energy surfaces, and multipath variational transition state theory with multidimensional tunneling, coupled-torsions anharmonicity, and high-frequency anharmonicity. We consider two different types of reaction mechanisms for the bimolecular reactions, namely, (i) addition-coupled hydrogen transfer and (ii) double hydrogen atom transfer (DHAT). First, we show that the MN15-L exchange-correlation functional has kJ/mol accuracy for the CH₂OO + H₂O and syn-CH₃CHOO + H₂O reactions. Then we show that, due to tunneling, the DHAT mechanism is especially important in the syn-CH₃CHOO + H₂O reaction. We show that the dominant pathways for reactions of Criegee intermediates depend on altitude. The results we obtain eliminate the discrepancy between experiment and theory under those conditions where experimental results are available, and we make predictions for the full range of temperatures and pressures encountered in the troposphere and stratosphere. The present results are an important cog in clarifying the atmospheric fate and oxidation processes of Criegee intermediates, and they also show how theoretical methods can provide reliable rate data for complex atmospheric processes.

Contrasting Effects of Water on the Barriers to Decarboxylation of Two Oxalic Acid Monohydrates: A Combined Rotational Spectroscopic and Ab Initio Study

Using rotational spectroscopy, we have observed two isomers of the monohydrate of oxalic acid, the most abundant dicarboxylic acid in the atmosphere. In the lowest-energy isomer, water hydrogen-bonds to both carboxylic acid groups, and the barrier to decarboxylation decreases. In the second isomer, water bonds to only one carboxylic acid group, and the barrier increases. Though the lower barrier in the former is not unequivocal evidence that water acts as a photocatalyst, the higher barrier in the latter indicates that water acts as an inhibitor in this topology. Oxalic acid is unique among dicarboxylic acids: for the higher homologues calculated, the inhibiting topology of the monohydrate is lowest in energy and most abundant under atmospheric conditions. Consequently, oxalic acid is the only dicarboxylic acid for which single-water catalysis of overtone-induced decarboxylation in the atmosphere is plausible.

Competition between H2O and (H2O)2 reactions with CH2OO/CH3CHOO

We calculated the bimolecular rate coefficients for the CH₂OO/CH₃CHOO reactions with H₂O/(H₂O)₂.

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

A rate coefficient is reported for the CH₂OO self-reaction and evidence presented for SO₂-catalysed CH₂OO isomerization or intersystem crossing.