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1. Radical–Radical Reaction Dynamics Probed Using Millimeterwave Spectroscopy: Propargyl + NH 2 /ND 2

   https://doi.org/10.1021/acs.jpclett.1c03813  

   Gurusinghe, Ranil M. ; Dias, Nureshan ; Mebel, Alexander M. ; Suits, Arthur G. ( January 2022 , The Journal of Physical Chemistry Letters)
2. OH, HO 2 , and RO 2 radical chemistry in a rural forest environment: measurements, model comparisons, and evidence of a missing radical sink

   https://doi.org/10.5194/acp-23-10287-2023  

   Bottorff, Brandon ; Lew, Michelle M. ; Woo, Youngjun ; Rickly, Pamela ; Rollings, Matthew D. ; Deming, Benjamin ; Anderson, Daniel C. ; Wood, Ezra ; Alwe, Hariprasad D. ; Millet, Dylan B. ; et al ( September 2024 , Atmospheric Chemistry and Physics)

   Abstract. The hydroxyl (OH), hydroperoxy (HO2), and organic peroxy (RO2)radicals play important roles in atmospheric chemistry. In the presence ofnitrogen oxides (NOx), reactions between OH and volatile organiccompounds (VOCs) can initiate a radical propagation cycle that leads to theproduction of ozone and secondary organic aerosols. Previous measurements ofthese radicals under low-NOx conditions in forested environmentscharacterized by emissions of biogenic VOCs, including isoprene andmonoterpenes, have shown discrepancies with modeled concentrations. During the summer of 2016, OH, HO2, and RO2 radical concentrationswere measured as part of the Program for Research on Oxidants:Photochemistry, Emissions, and Transport – Atmospheric Measurements ofOxidants in Summer (PROPHET-AMOS) campaign in a midlatitude deciduousbroadleaf forest. Measurements of OH and HO2 were made by laser-inducedfluorescence–fluorescence assay by gas expansion (LIF-FAGE) techniques,and total peroxy radical (XO2) mixing ratios were measured by the Ethane CHemical AMPlifier (ECHAMP) instrument. Supporting measurements ofphotolysis frequencies, VOCs, NOx, O3, and meteorological datawere used to constrain a zero-dimensional box model utilizing either theRegional Atmospheric Chemical Mechanism (RACM2) or the Master ChemicalMechanism (MCM). Model simulations tested the influence of HOxregeneration reactions within the isoprene oxidation scheme from the LeuvenIsoprene Mechanism (LIM1). On average, the LIM1 models overestimated daytimemaximum measurements by approximately 40 % for OH, 65 % for HO2,and more than a factor of 2 for XO2. Modeled XO2 mixing ratioswere also significantly higher than measured at night. Addition of RO2 + RO2 accretion reactions for terpene-derived RO2 radicals tothe model can partially explain the discrepancy between measurements andmodeled peroxy radical concentrations at night but cannot explain thedaytime discrepancies when OH reactivity is dominated by isoprene. Themodels also overestimated measured concentrations of isoprene-derivedhydroxyhydroperoxides (ISOPOOH) by a factor of 10 during the daytime,consistent with the model overestimation of peroxy radical concentrations.Constraining the model to the measured concentration of peroxy radicalsimproves the agreement with the measured ISOPOOH concentrations, suggestingthat the measured radical concentrations are more consistent with themeasured ISOPOOH concentrations. These results suggest that the models maybe missing an important daytime radical sink and could be overestimating therate of ozone and secondary product formation in this forest.

    

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3. Tunneling effects in the unimolecular decay of (CH 3 ) 2 COO Criegee intermediates to OH radical products

   https://doi.org/10.1063/1.4979297  

   Fang, Yi ; Barber, Victoria P. ; Klippenstein, Stephen J. ; McCoy, Anne B. ; Lester, Marsha I. ( April 2017 , The Journal of Chemical Physics)
4. A wealth of structures for the Ge 2 H 2 + radical cation: comparison of theory and experiment

   https://doi.org/10.1039/d3cp06098e  

   Poncelet, Ethan J ; Mull, Henry F ; Abate, Yohannes ; Robinson, Gregory H ; Douberly, Gary E ; Turney, Justin M ; Schaefer, Henry F ( April 2024 , Physical Chemistry Chemical Physics)

   From left to right and top to bottom, the five Ge₂H₂⁺structures are shown:trans, monobridged, butterfly, germylidene, and linear.

    

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5. CH 3 Radical Generation in Microplasmas for Up-Conversion of Methane

   https://doi.org/10.1021/acs.jpca.4c00073  

   Meyer, Mackenzie ; Kerketta, Sanjana ; Hartman, Ryan ; Kushner, Mark J ( April 2024 , The Journal of Physical Chemistry A)

   The conversion of methane, CH4, into higher value chemicals using low temperature plasmas is challenged by both improving efficiency and selectivity. One path towards selectivity is capturing plasma produced methyl radicals, CH3, in a solvent for aqueous processing. Due to the rapid reactions of methyl radicals in the gas phase, the transport distance from production of the CH3 to its solvation should be short, which then motivates the use of microplasmas. The generation of CH3 in Ar/CH4/H2O plasmas produced in nanosecond pulsed dielectric barrier discharge microplasmas is discussed using results from a computational investigation. The microplasma is sustained in the channel of a microfluidic chip in which the solvent flows along one wall or in droplets. CH3 is primarily produced by electron-impact of and dissociative excitation transfer to CH4, as well as CH2 reacting with CH4. CH3 is rapidly consumed to form C2H6 which, in spite of being subject to these same dissociative processes, accumulates over time, as do other stable products including C3H8 and CH¬3OH. The gas mixture and electrical properties were varied to assess their effects on CH3 production. CH3 production is largest with 5% CH4 in the Ar/CH4/H2O mixture due to an optimal balance of electron-impact dissociation, which increases with CH4 percentage, and dissociative excitation transfer and CH2 reacting with CH4, which decrease with CH4 percentage. Design parameters of the microchannels were also investigated. Increasing the permittivity of the dielectrics in contact with the plasma increased the ionization wave intensity which increased CH3 production. Increased energy deposition per pulse generally increased CH3 production as does lengthening pulse length up to a certain point. The arrangement of the solvent flow in the microchannel can also affect the CH3 density and fluence to the solvent. The fluence of CH3 to the liquid solvent is increased if the liquid is immersed in the plasma as a droplet or is a layer on the wall where the ionization wave terminates. The solvation dynamics of CH3 with varying numbers of droplets was also examined. The maximum density of solvated methyl radicals CH3aq occurs with a large number of droplets in the plasma. However, the solvated CH3aq density can rapidly decrease due to desolvation, emphasizing the need to quickly react the solvated species in the solvent. 

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