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1. H ₂ evolution from H ₂ O via O–H oxidative addition across a 9,10-diboraanthracene

   https://doi.org/10.1039/D0CC05261B  

   Taylor, Jordan W.; Harman, W. Hill (November 2020, Chemical Communications)

   null (Ed.)

   The water reactivity of the boroauride complex ([Au(B 2 P 2 )][K(18-c-6)]; (B 2 P 2 , 9,10-bis(2-(diisopropylphosphino)-phenyl)-9,10-dihydroboranthrene) and its corresponding two-electron oxidized complex, Au(B 2 P 2 )Cl, are presented. Au(B 2 P 2 )Cl is tolerant to H 2 O and forms the hydroxide complex Au(B 2 P 2 )OH in the presence of H 2 O and triethylamine. [Au(B 2 P 2 )]Cl and [Au(B 2 P 2 )]OH are poor Lewis acids as judged by the Gutmann–Becket method, with [Au(B 2 P 2 )]OH displaying facile hydroxide exchange between B atoms of the DBA ring as evidenced by variable temperature NMR spectroscopy. The reduced boroauride complex [Au(B 2 P 2 )] − reacts with 1 equivalent of H 2 O to produce a hydride/hydroxide product, [Au(B 2 P 2 )(H)(OH)] − , that rapidly evolves H 2 upon further H 2 O reaction to yield the dihydroxide compound, [Au(B 2 P 2 )(OH) 2 ] − . [Au(B 2 P 2 )]Cl can be regenerated from [Au(B 2 P 2 )(OH) 2 ] − via HCl·Et 2 O, providing a synthetic cycle for H 2 evolution from H 2 O enabled by O–H oxidative addition at a diboraanthracene unit. 

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2. 2D-imaging of absolute OH and H ₂ O ₂ profiles in a He–H ₂ O nanosecond pulsed dielectric barrier discharge by photo-fragmentation laser-induced fluorescence

   https://doi.org/10.1088/1361-6595/acaa53  

   van den Bekerom, Dirk; Tahiyat, Malik M; Huang, Erxiong; Frank, Jonathan H; Farouk, Tanvir I (January 2023, Plasma Sources Science and Technology)

   Abstract Pulsed dielectric barrier discharges (DBD) in He–H 2 O and He–H 2 O–O 2 mixtures are studied in near atmospheric conditions using temporally and spatially resolved quantitative 2D imaging of the hydroxyl radical (OH) and hydrogen peroxide (H 2 O 2 ). The primary goal was to detect and quantify the production of these strongly oxidative species in water-laden helium discharges in a DBD jet configuration, which is of interest for biomedical applications such as disinfection of surfaces and treatment of biological samples. Hydroxyl profiles are obtained by laser-induced fluorescence (LIF) measurements using 282 nm laser excitation. Hydrogen peroxide profiles are measured by photo-fragmentation LIF (PF-LIF), which involves photo-dissociating H 2 O 2 into OH with a 212.8 nm laser sheet and detecting the OH fragments by LIF. The H 2 O 2 profiles are calibrated by measuring PF-LIF profiles in a reference mixture of He seeded with a known amount of H 2 O 2 . OH profiles are calibrated by measuring OH-radical decay times and comparing these with predictions from a chemical kinetics model. Two different burst discharge modes with five and ten pulses per burst are studied, both with a burst repetition rate of 50 Hz. In both cases, dynamics of OH and H 2 O 2 distributions in the afterglow of the discharge are investigated. Gas temperatures determined from the OH-LIF spectra indicate that gas heating due to the plasma is insignificant. The addition of 5% O 2 in the He admixture decreases the OH densities and increases the H 2 O 2 densities. The increased coupled energy in the ten-pulse discharge increases OH and H 2 O 2 mole fractions, except for the H 2 O 2 in the He–H 2 O–O 2 mixture which is relatively insensitive to the additional pulses. 

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3. Rotational state-to-state transition rate coefficients for H ₂ O + H ₂ O collisions at nonequilibrium conditions

   https://doi.org/10.1051/0004-6361/202450738  

   Mandal, Bikramaditya; Zoltowski, Michal; Cordiner, Martin; Lique, Francois; Babikov, Dmitri (August 2024, Astronomy & Astrophysics)

   Aims.The goal is to develop a database of rate coefficients for rotational state-to-state transitions in H₂O + H₂O collisions that is suitable for the modeling of energy transfer in nonequilibrium conditions, in which the distribution of rotational states of H₂O deviates from local thermodynamic equilibrium. Methods.A two-temperature model was employed that assumed that although there is no equilibrium between all possible degrees of freedom in the system, the translational and rotational degrees of freedom can be expected to achieve their own equilibria independently, and that they can be approximately characterized by Boltzmann distributions at two different temperatures,T_kinandT_rot. Results.Upon introducing our new parameterization of the collisional rates, taking into account their dependence on bothT_kinandT_rot, we find a change of up to 20% in the H₂O rotational level populations for both ortho and para-H₂O for the part of the cometary coma where the nonequilibrium regime occurs. 

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4. Plasma-droplet interaction study to assess transport limitations and the role of ^⋅ OH, O ^⋅ ,H ^⋅ ,O ₂ (a ¹ Δ _g ),O ₃ , He(2 ³ S) and Ar(1s ₅ ) in formate decomposition

   https://doi.org/10.1088/1361-6595/ac2676  

   Nayak, Gaurav; Oinuma, Gaku; Yue, Yuanfu; Santos Sousa, João; Bruggeman, Peter J (November 2021, Plasma Sources Science and Technology)

   Abstract Plasmas interacting with liquid microdroplets are gaining momentum due to their ability to significantly enhance the reactivity transfer from the gas phase plasma to the liquid. This is, for example, critically important for efficiently decomposing organic pollutants in water. In this contribution, the role of ⋅ OH as well as non- ⋅ OH-driven chemistry initiated by the activation of small water microdroplets in a controlled environment by diffuse RF glow discharge in He with different gas admixtures (Ar, O 2 and humidified He) at atmospheric pressure is quantified. The effect of short-lived radicals such as O ⋅ and H ⋅ atoms, singlet delta oxygen (O 2 ( a 1 Δ g )), O 3 and metastable atoms of He and Ar, besides ⋅ OH radicals, on the decomposition of formate dissolved in droplets was analyzed using detailed plasma diagnostics, droplet characterization and ex situ chemical analysis of the treated droplets. The formate decomposition increased with increasing droplet residence time in the plasma, with ∼70% decomposition occurring within ∼15 ms of the plasma treatment time. The formate oxidation in the droplets is shown to be limited by the gas phase ⋅ OH flux at lower H 2 O concentrations with a significant enhancement in the formate decomposition at the lowest water concentration, attributed to e − /ion-induced reactions. However, the oxidation is diffusion limited in the liquid phase at higher gaseous ⋅ OH concentrations. The formate decomposition in He/O 2 plasma was similar, although with an order of magnitude higher O ⋅ radical density than the ⋅ OH density in the corresponding He/H 2 O plasma. Using a one-dimensional reaction–diffusion model, we showed that O 2 ( a 1 Δ g ) and O 3 did not play a significant role and the decomposition was due to O ⋅ , and possibly ⋅ OH generated in the vapor containing droplet-plasma boundary layer. 

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5. Reaction mechanism, energetics, and kinetics of the water-assisted thioformaldehyde + ˙OH reaction and the fate of its product radical under tropospheric conditions

   https://doi.org/10.1039/D0CP00570C  

   Arathala, Parandaman; Katz, Mark; Musah, Rabi A. (May 2020, Physical Chemistry Chemical Physics)

   The reactions of thioformaldehyde (H 2 CS) with OH radicals and assisted by a single water molecule have been investigated using high level ab initio quantum chemistry calculations. The H 2 CS + ˙OH reaction can in principle proceed through: (1) abstraction, and (2) addition pathways. The barrier height for the addition reaction in the absence of a catalyst was found to be −0.8 kcal mol −1 , relative to the separated reactants, which has a ∼1.0 kcal mol −1 lower barrier than the abstraction channel. The H 2 CS + ˙OH reaction assisted by a single water molecule reduces the barrier heights significantly for both the addition and abstraction channels, to −5.5 and −6.7 kcal mol −1 respectively, compared to the un-catalyzed H 2 CS + ˙OH reaction. These values suggest that water lowers the barriers by ∼6.0 kcal mol −1 for both reaction paths. The rate constants for the H 2 CS⋯H 2 O + ˙OH and OH⋯H 2 O + H 2 CS bimolecular reaction channels were calculated using Canonical Variational Transition state theory (CVT) in conjunction with the Small Curvature Tunneling (SCT) method over the atmospherically relevant temperatures between 200 and 400 K. Rate constants for the H 2 CS + ˙OH reaction paths for comparison with the H 2 CS + ˙OH + H 2 O reaction in the same temperature range were also computed. The results suggest that the rate of the H 2 CS + ˙OH + H 2 O reaction is slower than that of the H 2 CS + ˙OH reaction by ∼1–4 orders of magnitude in the temperatures between 200 and 400 K. For example, at 300 K, the rates of the H 2 CS + ˙OH + H 2 O and H 2 CS + ˙OH reactions were found to be 2.2 × 10 −8 s −1 and 6.4 × 10 −6 s −1 , respectively, calculated using [OH] = 1.0 × 10 6 molecules cm −3 , and [H 2 O] = 8.2 × 10 17 molecules cm −3 (300 K, RH 100%) atmospheric conditions. Electronic structure calculations on the H 2 C(OH)S˙ product in the presence of 3 O 2 were also performed. The results show that H 2 CS is removed from the atmosphere primarily by reacting with ˙OH and O 2 to form thioformic acid, HO 2 , formaldehyde, and SO 2 as the main end products. 

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