Imaging study of O3 photodissociation in the Huggins band

We report a velocity-mapped ion imaging study of the photodissociation of O3 in the Huggins band. The O(3PJ) images show evidence for three electronic channels producing O2(X3Σg-), O2(a1∆g), and O2(b1Σg+) state fragments, with the latter two arising from the spin-forbidden photodissociation of O3. Forward convolution simulations of the derived total translational energy distributions permit extraction of the vibrational state distribution for each O2 electronic state. All these distributions peak near v = 0 and decrease monotonically with the vibrational state. The wavelength-dependent branching of the three electronic channels has been determined and is approximately constant over the wavelength region studied (322-328 nm). We have observed that the O2 electronic state branching ratios depend on the coincident O(3PJ) spin-orbit state, and the O2(b1Σg+) state is particularly sensitive. These results are qualitatively consistent with previous calculations on the coupling of the initially excited state to dissociative states by Rosenwaks and Grebenshchikov [J. Phys. Chem. A. 114, 9809-9819 (2010)]. The spatial anisotropy of the three dissociation channels has been determined through analysis of the O(3P0) angular distributions. The results are consistent with recent calculations but differ from previous experimental reports. The experimental results provide detailed information on the dissociation dynamics and should motivate new calculations.

A rapid prototyped atmospheric non-thermal plasma-activated aerosol device and anti-bacterial characterisation

Non-plasma technologies are being extensively investigated for their potential to mitigate microbial growth through the production of various reactive species. Predominantly, studies utilise atmospheric non-thermal plasma to produce plasma-activated liquids. The advancement of plasma-liquid applications has led to the investigation of plasma-activated aerosols (PAAs). This study aimed to produce a rapid-prototyped plasma-activated aerosol setup and perform chemical and anti-bacterial characterisation on the resultant activated aerosols. The setup was produced using stereolithography 3D printing, and air was used as the carrier gas. The novel design of the device allowed for the direct production of PAAs without the prior generation of plasma-activated water and subsequent aerosolisation. The generated PAAs were assessed for nitrite, hydrogen peroxide and ozone content using colourimetric assays. Anti-bacterial efficacy was tested against three human pathogenic strains: Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Salmonella enterica. It was observed that nitrite and ozone contact concentration increased with exposure time, yet no hydrogen peroxide was detected. The generated PAAs showed significant zones of no growth for all bacterial strains. These devices, therefore, show potential to be used as anti-bacterial disinfection technologies.

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.

Potential energy surfaces for high-energy N + O2 collisions

Potential energy surfaces for high-energy collisions between an oxygen molecule and a nitrogen atom are useful for modeling chemical dynamics in shock waves. In the present work, we present doublet, quartet, and sextet potential energy surfaces that are suitable for studying collisions of O₂(³Σ_g ^-) with N(⁴S) in the electronically adiabatic approximation. Two sets of surfaces are developed, one using neural networks (NNs) with permutationally invariant polynomials (PIPs) and one with the least-squares many-body (MB) method, where a two-body part is an accurate diatomic potential and the three-body part is expressed with connected PIPs in mixed-exponential-Gaussian bond order variables (MEGs). We find, using the same dataset for both fits, that the fitting performance of the PIP-NN method is significantly better than that of the MB-PIP-MEG method, even though the MB-PIP-MEG fit uses a higher-order PIP than those used in previous MB-PIP-MEG fits of related systems (such as N₄ and N₂O₂). However, the evaluation of the PIP-NN fit in trajectory calculations requires about 5 times more computer time than is required for the MB-PIP-MEG fit.

Rate constants for collision-induced emission of O2(a1Δg) with He, Ne, Ar, Kr, N2, CO2 and SF6 as collisional partners

Rate constants for singlet oxygen collision induced emission of the a1Δg-X3Σ-g transition at 1.27 μm were measured for CO2, N2, SF6, and rare gases as collisional partners. Photolysis of ozone by 266 nm laser radiation produced singlet oxygen. We performed direct measurements of pressure dependences of the 1.27 μm emission intensity for partner gases. The measured rate constants kMa-X in the units of 10-24 cm3 s-1 are as follows: CO2 - 10 ± 2; N2 - 3.2 ± 0.6; SF6 - 7 ± 1; He - 1.1 ± 0.3; Ne - 1.3 ± 0.3; Ar - 2.8 ± 0.6; Kr - 6 ± 1. The measured values of kMa-X are close to the values calculated from absorption measurements. Considering the known rate constants kMb-a for the b1Σg+-a1Δg transition in the gas phase we found that the ratio kMa-X/kMb-a was constant and independent of a collisional partner according to the "spin-orbit based" mechanism of intensity borrowing proposed by Minaev (THEOCHEM, 1989, 183, 207). However, this ratio amounted to (1.3 ± 0.2) × 10-4, which is considerably lower than the theoretically predicted value of (3-6) × 10-4.