On the possibility of O₂(a ¹ _g) production by a non-self-sustained discharge for oxygen–iodine laser pumping

Abstract

O2(a 1Δg) production in a non-self-sustained discharge (ND) in pure oxygen and oxygen mixtures with inert gases (Ar and He) has been studied. A self-consistent model of ND in pure oxygen is developed, allowing us to simulate all the obtained experimental data. Agreement between the experimental and simulated results for pure oxygen over a wide range of reduced electric fields was reached only after taking into account the ion component of the discharge current. It is shown that the correct estimation of the energetic efficiency of O2(a 1Δg) excitation by discharge using the EEDF calculation is possible only with the correct description of the energy deposit into the plasma on the basis of an adequate discharge model. The testing of an O2(a 1Δg) excitation cross-section by direct electron impact, as well as a kinetic scheme of processes involving singlet oxygen, has been carried out by the comparison of experimental and simulated data. The tested model was then used for simulating O2(a 1Δg) production in ND in oxygen mixtures with inert gases. The study of O2(a 1Δg) production in Ar : O2 mixtures with small oxygen content has shown that the ND in these mixtures is spatially non-uniform, which essentially decreases the energetic efficiency of singlet oxygen generation. While simulating the singlet oxygen density dynamics, the process of three-body deactivation of O2(a 1Δg) by O(3P) atoms was for the first time taken into account. The maximal achievable concentration of singlet oxygen in ND can be limited by this quenching. On the basis of the results obtained and the model developed, the influence of hydrogen additives on singlet oxygen kinetics in argon–oxygen–hydrogen mixtures has been analysed. The simulation has shown that fast quenching of O2(a 1Δg) by atomic hydrogen is possible due to significant gas heating in the discharge that can significantly limit the yield of singlet oxygen in hydrogen-containing mixtures.

Recent advances in the development of discharge‐pumped oxygen‐iodine lasers

“…In addition to the expected emission from I*, bright visible fluorescence from the I B-X transition was also present. The latter was not seen for the same flow conditions without the wall coating due to the rapid removal of I by O atom reactions (14) and (15). Detection of the B-X emission implies that the wall-catalyzed production of O (a) consumes O atoms, but the mechanism of this reaction is not yet known.…”

“…Extensive modeling of O discharges has been used to explore the optimum conditions for producing high yields and high concentrations of O (a) [3,[12][13][14][15][16][17]. One of the limitations imposed by the discharge environment is that O (a) is both generated and destroyed by electron impact processes.…”

“…Rakhimova and co-workers [14,15,27] proposed that threebody deactivation was responsible for a decrease in O (a) yield that was observed as they raised the pressure of their RF discharge source. As high-pressure operation of the discharge generators will be needed for high power devices, control and characterization of the three-body deactivation channels is an important issue.…”

“…Since then, Carroll and co-workers have made significant advances in the development of RF discharges for O (a) production [35]. Building on fundamental plasma studies [14][15][16][17]27,[36][37][38][39][40][41], they have investigated the effects of discharge frequency, geometry and electrode length on the yield and power loading. Capacitively coupled transverse discharges with small electrode gaps were found to be most effective.…”

Initiation of combustion of a CH4-O2 mixture in a supersonic flow with excitation of O2 molecules by an electric discharge

“…O 2 (b 1 Σ + g ) molecules. Recent theoretical and experimental studies of physical and chemical processes in oxygen plasma generated by a non-self-sustained discharge [10][11][12][13][14][15] showed that significant amounts of singlet oxygen O 2 (a 1 Δ g ) and O 2 (b 1 Σ + g ) molecules (≈4%) can be obtained even at pressures close to the atmospheric value. In contrast to excitation of O 2 molecules by laser radiation, the plasma in the electric discharge always contains small amounts of atomic oxygen (O) and ozone molecules (O 3 ), as well as vibrationally excited O 2 molecules in the ground electronic state [10][11][12][13].…”