Effect of the nonlocal nature of the electron energy spectrum on the dissociation of oxygen molecules in a discharge

Klopovskiy, K.S.; Lopaev, Dmitry; Proshina, O. V.; Rakhimov, A. T.; Рахимова, Т. В.

doi:10.1134/1.1768587

Cited by 11 publications

(19 citation statements)

References 13 publications

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“…This is preferable to using the O atom density since in this case the effect of gas temperature variations on the total gas density, N, are eliminated. The [O]/N variations were followed by time-resolved actinometry, using Ar (added as 5% of the gas flow) as the actinometer gas [1,3,4,6,[9][10][11]13,[35][36][37][38][39][40][41][42]. The effect of this small addition of Ar on the EEDF and other discharge parameters is negligible, since the EEDF is largely determined by electron collisions with the majority gas, O 2 [43].…”

Section: Measurement Of the O Atom Density Loss Frequency And Surfacmentioning

confidence: 99%

Oxygen (³P) atom recombination on a Pyrex surface in an O₂ plasma

Booth

Guaitella

Chatterjee

et al. 2019

Plasma Sources Sci. Technol.

258

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The recombination of O (3 P) atoms on the surface of a Pyrex tube containing a DC glow discharge in pure O 2 was studied over a wide range of pressure (0.2-10 Torr) and discharge current (10-40 mA) for two fixed surface temperatures (+50°C and +5°C). The recombination probability, , was deduced from the observed atom loss rate (dominated by surface recombination) determined by time-resolved optical emission actinometry in partially-modulated (amplitude ~15-17%) discharges. The value of  increased with discharge current at all pressures studied. As a function of pressure it passes through a minimum at ~0.75 Torr. At pressures above this minimum  is well-correlated with the gas temperature, T g , (determined from the rotational structure of the O 2 (b 1  g + ,v=0)  O 2 (X 3  g-,v=0) emission spectrum) which increases with pressure and current. The temperature of the atoms incident at the surface was deduced from a model, calibrated by measurements of the spatially-averaged gas temperature and validated by radial temperature profile measurements. The value of  follows an Arrhenius law depending on the incident atom temperature, with an activation energy in the range 0.13-0.16 eV. At the higher surface temperature the activation energy is the same, but the pre-exponential factor is smaller. Under conditions where the O flux to the surface is low  falls below this Arrhenius law. These results are well explained by an Eley-Rideal (ER) mechanism with incident O atoms recombining with both chemisorbed and more weakly bonded physisorbed atoms on the surface, with the kinetic energy of the incident atoms providing the energy to overcome the activation energy barrier. A phenomenological Eley-Rideal model is proposed that explains both the decrease in recombination probability with surface temperature as well as the deviations from the Arrhenius law when the O flux is low. At pressures below 0.75 Torr  increases significantly, and also increases strongly with the discharge current. We attribute this effect to incident ions and fast neutrals arriving with sufficient energy to clean or chemically modify the surface, generating new adsorption sites. Discharge modeling confirms that at pressures below ~0.3 Torr a noticeable fraction of the ions arriving at the surface have adequate kinetic energy to break surface chemical bonds (> 3-5 eV).

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Section: Measurement Of the O Atom Density Loss Frequency And Surfacmentioning

confidence: 99%

Oxygen (³P) atom recombination on a Pyrex surface in an O₂ plasma

Booth

Guaitella

Chatterjee

et al. 2019

Plasma Sources Sci. Technol.

258

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“…The O(3p 5 P → 3p 5 S) at λ = 777.1 nm and Ar(2p 1 -1s 2 ) at λ = 750.4 nm transitions were used. These transitions are typical for oxygen atom actinometry, when the contribution of dissociative excitation to the 777.1 nm emission is accounted for, based on the following formulae, valid for a stationary discharge [21,23,25,26]:…”

Section: Experimental Principlesmentioning

confidence: 99%

“…where ν ij , A ij and ν nm , A nm -frequencies and Einstein's coefficients for oxygen and argon atoms, respectively; k O e and k Ar e -rate constants of electron impact excitation of emitting states O * and Ar * , respectively; k The electron impact rate constants in equations (2) and (3) were calculated using a self-consistent model of a dc glow discharge in pure oxygen [14,[23][24][25]. The EEDF as a function of radial position was found self-consistently by a particlein-cell/Monte-Carlo (PIC/MC) technique or by solving the non-local Boltzmann equation [14,[23][24][25]. Oxygen atoms and singlet oxygen molecules have long lifetimes, resulting in relatively high density of these species in the discharge, which can influence the electron density, electric field and EEDF via detachment reactions with negative ions.…”

Section: Measurement Of Concentration and Dynamics Of Atomic Oxygenmentioning

confidence: 99%

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Negative ion destruction by O(³P) atoms and O₂(a ¹Δ_g) molecules in an oxygen plasma

Belostotsky

Economou

Lopaev

et al. 2005

Plasma Sources Sci. Technol.

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Laser photodetachment was used to investigate the dynamics of negative ion density in the positive column of a pure oxygen dc glow discharge over a range of pressure (0.1-5 Torr) and current density (2-40 mA cm −2). Upon discharge current modulation, the negative ion O − concentration decayed with the characteristic loss times of oxygen O(3 P) atom and metastable oxygen O 2 (a 1 g) molecule concentrations over a wide range of discharge parameters. To determine the rate constants of negative ion loss by reaction with these species, the dynamics of O(3 P) atoms and O 2 (a 1 g) molecules was investigated using time-resolved actinometry and IR spectroscopy at 1.27 µm, respectively. At pressures greater than ∼0.5 Torr the attachment-detachment dominated regime of the oxygen discharge was realized and the main negative ion was O −. Under these conditions, electron attachment to O 2 molecules to produce O − was compensated by detachment of O − with O(3 P) and O 2 (a 1 g). The rate constants of O − detachment with O(3 P) atoms (O − + O(3 P) → O 2 + e: k O d = (2.3 ± 0.5) × 10 −10 cm 3 s −1) and singlet O 2 (a 1 g) molecules (O − + O 2 (a 1 g) → products + e: k d = (1.9 ± 0.4) × 10 −10 cm 3 s −1), were determined in the plasma itself for the first time.

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“…To date there have been no direct measurements of this rate constant. Reaction (1) can also play a significant role in the balance of singlet oxygen in the Earth's atmosphere [13].…”

Section: Introductionmentioning

confidence: 99%