[en] An experimental study has been carried out of the kinetics of formation of singlet oxygen molecules in the a¹Δ_g state in a decaying oxygen-nitrogen plasma. The oxygen-nitrogen medium at pressures of 10 and 20 torr was excited by rf discharges. The mass fraction of oxygen varied from 2.5 to 100%. The O₂(a¹Δ_g) concentration was determined from the spontaneous emission at wavelength λ = 1268 nm. The experimental device could be operated in two ways: either by exciting a previously prepared nitrogen-oxygen mixture with an rf discharge or by independently using rf discharges to excite streams of nitrogen and oxygen, which were then mixed. The experiments showed that there exists an efficient process for transmitting vibrational energy of the nitrogen molecules to the metastable electron state a¹Δ_g of the oxygen molecules in which this mechanism acts through intermediate strong excitation of the vibrational modes of ozone. Nonmonatomic quenching of O₂(a¹Δ_g) by ozone has been observed, which is also associated with vibrational excitation of O₃. It has been shown experimentally that the O₃(vib) molecules form through interaction with vibrationally excited nitrogen molecules and in three-body reactions converting atomic oxygen to ozone. These results can be important for understanding the properties of ozone generation and the excitation of oxygen states in plasma-chemical devices of various types, and also for interpreting experimental data in the physics of the upper atmosphere. 17 refs., 7 figs

[en] A method is proposed for measuring the probabilities of the heterogeneous loss of radicals in a gas-discharge plasma. The method is based on the time-resolved modulation actinometry. It is shown that this method is applicable for O, H, F, and CF₂ radicals. The probabilities of the loss of these radicals on the discharge tube wall are measured in a dc glow discharge. It is shown that the measurement results do not depend on which radical's emission line is used. The measurement results are only slightly affected by the dissociative excitation of the radical's emitting states and the background emission from the plasma. It is shown that the technique proposed is similar to the method of laser-induced fluorescence and provides a fairly high accuracy when measuring the probabilities (up to γ_R ∼ 10^-2-10^-1) of the surface loss of radicals in a gas-discharge plasma. In contrast to the LIF method, this technique allows one to acquire a large amount of experimental data over a reasonable time interval (up to one thousand of γ_R measurements per hour). This feature is an important and necessary condition for a thorough study of the surface reactions and the complicated many-parametrical mechanism for the heterogeneous loss of radicals

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[en] Quenching of O₂(^1Δ_g) molecules both in the gas phase and on a reactor surface has been investigated in binary mixtures of hydrogen and oxygen by using the fast-flow quartz reactor and infrared emission spectroscopy. Rate constants of the O₂(^1Δ_g) deactivation by H₂ and O₂ at room temperature have been determined to be (1.5±0.5) 10^-18 cm³ s^-1 and (1.6±0.2) 10^-18 cm³ s^-1, respectively. Heterogeneous quenching of O₂(^1Δ_g) on quartz walls has been studied both in pure oxygen and in H₂:O₂ mixtures. A model of O₂(^1Δ_g) heterogeneous quenching in binary mixtures has been developed and has allowed us to describe all observed features of singlet oxygen kinetics. Active surface complexes formed by 'chemisorbed' atomic oxygen and 'physadsorbed' molecules of O₂ and H₂ are assumed to be responsible for the O₂(^1Δ_g) heterogeneous deactivation. It has been shown that the higher rate of O₂(^1Δ_g) quenching in pure oxygen is connected with a quasi-resonant transfer of the O₂(^1Δ_g) electronic excitation to physadsorbed oxygen molecules. The observed effect of the wall passivation by hydrogen is conditioned both by the absence of the similar resonance in the hydrogen surface complex and by the higher bond energy of H₂ in this complex. Bond energies of O₂ (3750±450 K) and H2 (4050±450 K) in the surface complexes have been determined from the model parameters by fitting calculations to experimental results. (author)

[en] The effect of electron distribution function nonlocality on the oxygen dissociation rate in the glow discharge is studied. The oxygen atoms concentrations are measured in dependence on the discharge parameters. The analysis of the obtained data made it possible to study in detail the oxygen atoms balance in the discharge. It is shown, that the atoms formation and thus their concentration in the plasma volume, obtained in the case of accounting for the electrons distribution function nonlocality by energy, agree well with the experimental data

[en] The effect of the nonlocal nature of the electron distribution function on the dissociation rate of oxygen molecules in a dc glow discharge is studied. The concentration of oxygen atoms and the probability of their loss at the discharge tube wall are measured as functions of the discharge parameters by means of the time-resolved actinometric method involving argon atoms. An analysis of the measurement data in terms of both a discharge model in which the effect of the nonlocal nature of the electron energy spectrum is taken into account and a model in which this effect is ignored makes it possible to thoroughly investigate the balance of oxygen atoms in the discharge. The production rate of O(³P) atoms and their concentration in the plasma are calculated with allowance for the nonlocal nature of the electron energy distribution function. The calculated values agree well with the experimental data and differ substantially from those obtained using a spatially homogeneous distribution function

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No abstract available

[en] Results are presented from measurements of the density of oxygen atoms in the positive column of a dc discharge in pure oxygen by the actinometric technique using Ar atoms. Based on the excitation rate constants calculated using two different approaches (namely, the two-term approximation and the Monte Carlo method) to solving the Boltzmann equation for a spatially inhomogeneous electron distribution function, the applicability of the actinometric technique is analyzed. The effects of the discharge kinetics and the nonlocal character of the electron energy spectrum on the accuracy of actinometric measurements are studied. It is shown that the results of measurements depend only slightly on the accuracy with which the electron energy distribution function is described. Over a wide range of the reduced electric field E/N ≅ 40-250 Td, the oxygen atom density calculated using the spatially homogeneous distribution function differs by several percent from that calculated accurately, taking into account the nonlocal character of the electron energy spectrum. It is shown that using the actinometric technique to measure the absolute concentration of oxygen atoms in a plasma requires a detailed description of the discharge plasmochemical kinetics, including a thorough analysis of all possible processes (particularly, surface heterogeneous reactions) that determine the density of active particles at low pressures. At the same time, the use of the actinometric technique for monitoring the behavior of the density of oxygen atoms in a plasma is justified over a wide range of reduced electric fields up to ∼200 Td when the O(3p³P-3p³S) transition (λ = 844.6 nm) is used and the degree of dissociation is [O]/[O₂] > 0.02