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1. Formic acid catalyzed isomerization and adduct formation of an isoprene-derived Criegee intermediate: experiment and theory

   https://doi.org/10.1039/d0cp05018k  

   Vansco, Michael F. ; Caravan, Rebecca L. ; Pandit, Shubhrangshu ; Zuraski, Kristen ; Winiberg, Frank A. ; Au, Kendrew ; Bhagde, Trisha ; Trongsiriwat, Nisalak ; Walsh, Patrick J. ; Osborn, David L. ; et al ( December 2020 , Physical Chemistry Chemical Physics)

   null (Ed.)

   Isoprene is the most abundant non-methane hydrocarbon emitted into the Earth's atmosphere. Ozonolysis is an important atmospheric sink for isoprene, which generates reactive carbonyl oxide species (R 1 R 2 CO + O − ) known as Criegee intermediates. This study focuses on characterizing the catalyzed isomerization and adduct formation pathways for the reaction between formic acid and methyl vinyl ketone oxide (MVK-oxide), a four-carbon unsaturated Criegee intermediate generated from isoprene ozonolysis. syn -MVK-oxide undergoes intramolecular 1,4 H-atom transfer to form a substituted vinyl hydroperoxide intermediate, 2-hydroperoxybuta-1,3-diene (HPBD), which subsequently decomposes to hydroxyl and vinoxylic radical products. Here, we report direct observation of HPBD generated by formic acid catalyzed isomerization of MVK-oxide under thermal conditions (298 K, 10 torr) using multiplexed photoionization mass spectrometry. The acid catalyzed isomerization of MVK-oxide proceeds by a double hydrogen-bonded interaction followed by a concerted H-atom transfer via submerged barriers to produce HPBD and regenerate formic acid. The analogous isomerization pathway catalyzed with deuterated formic acid (D 2 -formic acid) enables migration of a D atom to yield partially deuterated HPBD (DPBD), which is identified by its distinct mass ( m / z 87) and photoionization threshold. In addition, bimolecular reaction of MVK-oxide with D 2 -formic acid forms a functionalized hydroperoxide adduct, which is the dominant product channel, and is compared to a previous bimolecular reaction study with normal formic acid. Complementary high-level theoretical calculations are performed to further investigate the reaction pathways and kinetics. 

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2. Electronic Absorption Spectroscopy and Photochemistry of Criegee Intermediates

   https://doi.org/10.1111/php.13665  

   Karsili, Tolga N. V. ; Marchetti, Barbara ; Lester, Marsha I. ; Ashfold, Michael N. R. ( July 2022 , Photochemistry and Photobiology)

   Interest in Criegee intermediates (CIs), often termed carbonyl oxides, and their role in tropospheric chemistry has grown massively since the demonstration of laboratory‐based routes to their formation and characterization in the gas phase. This article reviews current knowledge regarding the electronic spectroscopy of atmospherically relevant CIs like CH₂OO, CH₃CHOO, (CH₃)₂COO and larger CIs like methyl vinyl ketone oxide and methacrolein oxide that are formed in the ozonolysis of isoprene, and of selected conjugated carbene‐derived CIs of interest in the synthetic chemistry community. Of the aforementioned atmospherically relevant CIs, all except CH₂OO and (CH₃)₂COO exist in different conformers which, under tropospheric conditions, can display strikingly different thermal loss ratesviaunimolecular and bimolecular processes. Calculated photolysis rates based on their absorption properties suggest that solar photolysis will rarely be a significant contributor to the total loss rate for any CI under tropospheric conditions. Nonetheless, there is ever‐growing interest in the absorption cross sections and primary photochemistry of CIs following excitation to the strongly absorbing¹ππ* state, and how this varies with CI, with conformer and with excitation wavelength. The later part of this review surveys the photochemical data reported to date, including a range of studies that demonstrate prompt photo‐induced fission of the terminal O–O bond, and speculates about possible alternate decay processes that could occur following non‐adiabatic coupling to, and dissociation from, highly internally excited levels of the electronic ground state of a CI.

    

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3. Functionalized Hydroperoxide Formation from the Reaction of Methacrolein-Oxide, an Isoprene-Derived Criegee Intermediate, with Formic Acid: Experiment and Theory

   https://doi.org/10.3390/molecules26103058  

   Vansco, Michael F. ; Zuraski, Kristen ; Winiberg, Frank A. ; Au, Kendrew ; Trongsiriwat, Nisalak ; Walsh, Patrick J. ; Osborn, David L. ; Percival, Carl J. ; Klippenstein, Stephen J. ; Taatjes, Craig A. ; et al ( May 2021 , Molecules)

   null (Ed.)

   Methacrolein oxide (MACR-oxide) is a four-carbon, resonance-stabilized Criegee intermediate produced from isoprene ozonolysis, yet its reactivity is not well understood. This study identifies the functionalized hydroperoxide species, 1-hydroperoxy-2-methylallyl formate (HPMAF), generated from the reaction of MACR-oxide with formic acid using multiplexed photoionization mass spectrometry (MPIMS, 298 K = 25 °C, 10 torr = 13.3 hPa). Electronic structure calculations indicate the reaction proceeds via an energetically favorable 1,4-addition mechanism. The formation of HPMAF is observed by the rapid appearance of a fragment ion at m/z 99, consistent with the proposed mechanism and characteristic loss of HO2 upon photoionization of functional hydroperoxides. The identification of HPMAF is confirmed by comparison of the appearance energy of the fragment ion with theoretical predictions of its photoionization threshold. The results are compared to analogous studies on the reaction of formic acid with methyl vinyl ketone oxide (MVK-oxide), the other four-carbon Criegee intermediate in isoprene ozonolysis. 

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4. Sulfur Dioxide Modifies Aerosol Particle Formation and Growth by Ozonolysis of Monoterpenes and Isoprene

   https://doi.org/10.1029/2018JD030064  

   Stangl, Christopher M. ; Krasnomowitz, Justin M. ; Apsokardu, Michael J. ; Tiszenkel, Lee ; Ouyang, Qi ; Lee, Shanhu ; Johnston, Murray V. ( April 2019 , Journal of Geophysical Research: Atmospheres)

   The effect of sulfur dioxide on particle formation and growth by ozonolysis of three monoterpenes (α‐pinene,β‐pinene, and limonene) and isoprene was investigated in the presence of monodisperse ammonium sulfate seed particles and an OH scavenger in a flow tube under dry conditions. Without sulfur dioxide, new particle formation was not observed, and seed particle growth was consistent with condensation of low‐volatility oxidation products produced from each organic precursor. With sulfur dioxide, new particle formation was observed from every precursor studied, consistent with sulfuric acid formation by reaction of sulfur dioxide with stabilized Criegee Intermediates. The presence of sulfur dioxide did not significantly affect seed particle growth rates fromα‐pinene and limonene ozonolysis, although chemical composition measurements revealed the presence of organosulfates in the particles following SO₂exposure. Contrarily, the growth of seeds byβ‐pinene and isoprene ozonolysis was considerably enhanced by sulfur dioxide, and chemical composition measurements revealed that the enhanced growth was not due to additional organic material, suggesting that inorganic sulfate was likely responsible. The results suggest that a previously unconsidered particle‐phase pathway to growth activated by sulfur dioxide may alter production of cloud condensation nuclei over regions with significant SO₂‐alkene interactions.

    

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5. Quantitative constraints on autoxidation and dimer formation from direct probing of monoterpene-derived peroxy radical chemistry

   https://doi.org/10.1073/pnas.1812147115  

   Zhao, Yue ; Thornton, Joel A. ; Pye, Havala O. T. ( November 2018 , Proceedings of the National Academy of Sciences)

   Organic peroxy radicals (RO₂) are key intermediates in the atmospheric degradation of organic matter and fuel combustion, but to date, few direct studies of specific RO₂in complex reaction systems exist, leading to large gaps in our understanding of their fate. We show, using direct, speciated measurements of a suite of RO₂and gas-phase dimers from O₃-initiated oxidation of α-pinene, that ∼150 gaseous dimers (C_16–20H_24–34O_4–13) are primarily formed through RO₂cross-reactions, with a typical rate constant of 0.75–2 × 10⁻¹²cm³molecule⁻¹s⁻¹and a lower-limit dimer formation branching ratio of 4%. These findings imply a gaseous dimer yield that varies strongly with nitric oxide (NO) concentrations, of at least 0.2–2.5% by mole (0.5–6.6% by mass) for conditions typical of forested regions with low to moderate anthropogenic influence (i.e., ≤50-parts per trillion NO). Given their very low volatility, the gaseous C_16–20dimers provide a potentially important organic medium for initial particle formation, and alone can explain 5–60% of α-pinene secondary organic aerosol mass yields measured at atmospherically relevant particle mass loadings. The responses of RO₂, dimers, and highly oxygenated multifunctional compounds (HOM) to reacted α-pinene concentration and NO imply that an average ∼20% of primary α-pinene RO₂from OH reaction and 10% from ozonolysis autoxidize at 3–10 s⁻¹and ≥1 s⁻¹, respectively, confirming both oxidation pathways produce HOM efficiently, even at higher NO concentrations typical of urban areas. Thus, gas-phase dimer formation and RO₂autoxidation are ubiquitous sources of low-volatility organic compounds capable of driving atmospheric particle formation and growth.

    

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