Product channels of the reactions of O2(b1 Σg+ )

State-resolved modeling of electronic excitation in weakly ionized oxygen mixtures

Electronic excitation and ionization in oxygen-argon mixtures are analyzed using a three-temperature electronic state-resolved model and evaluated using recent experimental data from reflected shock experiments. A detailed description of the model formulation and parameter selection is provided. Excellent agreement is obtained between model predictions and experimental measurements of O_{2} number density during dissociation in mixtures of 2%-5% O_{2} dilute in argon. Next, electron number density measurements are leveraged to infer a rate constant for the heavy particle impact excitation of argon, facilitating improved modeling of net ionization and a clearer understanding of the electronic excitation kinetics of oxygen. The electronic state-resolved model is then assessed using measured data for three electronic states of atomic oxygen. The model successfully reproduces the multistage behavior observed in the measured time histories and yields new insights into the multistage behavior that revises previous interpretations. For several experiments, the modeling choices involved in the calculation of escape factors significantly influence the predicted time histories. A global sensitivity analysis considering nearly 300 parameters is then conducted to identify which model parameters most sensitively influence the predicted excited state populations. Excitation of the measured states from the metastable levels and collisional excitation between the three measured states are important across all conditions. The excited state populations demonstrate complex sensitivities involving a large number of collisional and radiative processes, highlighting the importance of adopting a detailed modeling approach when interpreting excited state measurements.

Ozone destruction due to the recombination of oxygen atoms

Kinetics of ozone destruction due to the recombination of oxygen atoms produced by pulsed 266 nm laser photolysis of O₃/M (M = CO₂ and/or N₂) mixtures was studied using the absorption and emission spectroscopy to follow time evolutions of O₃ and electronically excited molecules O₂* formed in the recombination process 2O(³P) + M → O₂* + M. An unexpected high ozone destruction rate was observed when O₂* was present in the system. The kinetic model developed for the oxygen nightglow on the terrestrial planets was adapted to interpret the detected temporal profiles of the ozone number density and the O₂* emission intensities. It was deduced that the vibrationally excited singlet delta oxygen molecule O₂(a¹Δ, υ) formed in the secondary processes reacts efficiently with ozone in the process O₂(a¹Δ, υ ≥ 3) + O₃ → 2O₂ + O, and the rate constant of this process was estimated to be 3 × 10^-11 cm³ s^-1. Ab initio calculations at the CASPT2(14, 12)/cc-pVTZ/UωB97XD/cc-pVTZ level of theory were applied to find the reaction pathway from the reactants to products on the O₅ potential energy surface. These calculations revealed that the O₂(a¹Δ) + O₃ reaction is likely to proceed via singlet-triplet intersystem crossing exhibiting an energy barrier of 9.6 kcal/mol, which lies between two and three quanta of vibrational excitation of O₂(a¹Δ), and hence, O₂(a¹Δ, υ) with υ ≥ 3 could rapidly react with ozone.