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1. Ultraviolet photodissociation of 2-methylallyl radical

   https://doi.org/10.1063/1674-0068/cjcp2309088  

   Lucas, Michael; Qin, Yuan; Chen, Min; Sun, Ge; Zhang, Jingsong (April 2024, Chinese Journal of Chemical Physics)

   Ultraviolet photodissociation dynamics of 2-methylallyl radical from the 3p Rydberg state were investigated in the wavelength region of 226–244 nm using the high-n Rydberg atom time-of-flight (HRTOF) technique. The 2-methylallyl radicals were generated by 193 nm photolysis of 3-chloro-2-methyl-1-propene precursors. The photofragment yield spectrum of H-atom products increases in intensity with decreasing wavelengths in 226–244 nm. The TOF spectra of H-atom products show a bimodal structure. The predominant product channel (with ∼98% branching ratio) has a kinetic energy release peaking at ∼7 kcal/mol, with an average ratio of ET in the total available energy, (fT), of ∼0.18 in 226–244 nm and an isotropic product angular distribution. At the low ET, isotropic component is from statistical unimolecular decomposition of highly vibrationally excited hot 2-methylallyl to the methylenecyclopropane+H products, following internal conversion from the excited electronic state. The minor product channel (with ∼2% branching ratio) has a large kinetic energy peaking at ∼50 kcal/mol, with (fT)≈0.63 and an anisotropic angular distribution (β≈−0.2). At the high ET, anisotropic component is non-statistical and is postulated to be from direct loss of H atom via the 3p Rydberg state or repulsive part of the ground state to the 1,3-butadiene+H products. 

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2. 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)
3. Kinetic study of the CN radical reaction with 2‐methylfuran

   https://doi.org/10.1002/kin.21403  

   Lee, James; Caster, Kacee; Maddaleno, Trey; Donnellan, Zachery; Selby, Talitha M.; Goulay, Fabien (July 2020, International Journal of Chemical Kinetics)

   Abstract The gas phase reaction of the ground state cyano‐radical (CN (X²∑⁺)) with 2‐methylfuran (2‐MF) is investigated in a quasi‐static reaction cell at pressures ranging from 2.2 to 7.6 Torr and temperatures ranging from 304 to 440 K. The CN radicals are generated in their ground electronic state by pulsed laser photolysis of gaseous cyanogen iodide (ICN) at 266 nm. Their concentration is monitored as a function of reaction time using laser‐induced fluorescence at 387.3 nm on the B²∑⁺(ν′ = 0) ← X²∑⁺(ν″ = 0) vibronic band. The reaction rate coefficient is found to be rapid and independent of pressure and temperature. Over the investigated temperature and pressure ranges, the rate coefficient is measured to be 2.83 (± 0.18) × 10⁻¹⁰cm³molecules s⁻¹. The enthalpies of the stationary points and transition states on the CN + 2‐MF potential energy surface are calculated using the CBS‐QB3 computational method. The kinetic results suggest the lack of a prereactive complex on the reaction entrance channel with either a very small or nonexistent entrance energy barrier. In addition, the potential energy surface calculations reveal only submerged barriers along the minimum energy path. Based on comparisons between previous CN reactions with unsaturated hydrocarbons, the most likely reaction pathway is CN addition onto one of the unsaturated carbons followed by either H or methyl elimination. The implications for the transformation of biomass‐derived fuels in nitrogen‐rich flames is discussed. 

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4. Synthesis of Tryptamines from Radical Cyclization of 2-Iodoaryl Allenyl Amines and Coupling with 2-Azallyls

   https://doi.org/10.1021/acs.joc.2c00767  

   Wang, Bo; Li, Minyan; Gao, Gui; Sanz-Vidal, Alvaro; Zheng, Bing; Walsh, Patrick J. (June 2022, The Journal of Organic Chemistry)
5. 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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