Heterogeneous quenching of O2(1Deltag) molecules in H2:O2mixtures

Klopovskiy, K.S.; Lopaev, Dmitry; Попов, Н. А.; Rakhimov, A. T.; Рахимова, Т. В.

doi:10.1088/0022-3727/32/23/305

Cited by 31 publications

(29 citation statements)

References 26 publications

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“…The potential drop across the sheath corresponds to the difference between plasma and floating potentials. This difference is always of the order of the ionization potential [57,58], since the creation rate of electrons in the bulk (requiring at least the ionization energy) must be equal to the ion flux leaving the plasma through the sheath to the floating walls. So, to estimate the IEDF at the wall a typical value of ~1.5O 2 ionization potential (~18 eV) was taken as the voltage drop across the sheath.…”

Section: Recombination Probability At Pressures Below 075 Torrmentioning

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: Recombination Probability At Pressures Below 075 Torrmentioning

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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“…Atomic oxygen can be lost by recombination on the plasma containing wall and singlet molecules can deactivate on this wall. The loss probabilities for atoms γ O and singlet oxygen molecules γ on glass and fused quartz are quite low, γ O ≈ 10 −3 and γ ≈ 10 −4 [21,22]. For that reason, the radius of the discharge tube (R = 0.6 cm) is much less than the characteristic length of O( 3 P) or O 2 (a 1 g ) loss, loss ≈ 2.4 √ Dτ loss ∼ 10-100 cm (Ddiffusion coefficient, τ loss -wall loss lifetime).…”

Section: Experimental Principlesmentioning

confidence: 99%

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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“…The surface deactivation efficiency of O 2 a 1 Δ g on quartz and silica is reported to be on the order of 10 −4 to 10 −5 at room temperature [17,45].…”

Section: Discussionmentioning

confidence: 99%

Singlet Molecular Oxygen Formation by O-Atom Recombination on Fused-Quartz Surfaces

White

Copeland

Marschall

2015

Journal of Thermophysics and Heat Transfer

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Experimental results demonstrate O 2 a 1 Δ g (υ 0) formation by catalytic O-atom surface recombination in a room-temperature fused-quartz flow-tube reactor. Resonance-enhanced multiphoton ionization is used to detect O 2 a 1 Δ g (υ 0) downstream of a nitrogen discharge flow titrated with nitric oxide to introduce oxygen atoms. A calibration procedure based on ozone photodissociation is developed to quantify O 2 a 1 Δ g (υ 0) resonanceenhanced multiphoton ionization signals. Partial pressures of O 2 a 1 Δ g (υ 0) in the range of 2.9 to 14 μtorr are measured in the ionization cell for O-atom partial pressures of 1.4-2.9 mtorr atomic oxygen introduced at the titration port. O 2 a 1 Δ g (υ 1) could not be detected; an upper limit for the O 2 a 1 Δ g (υ 1) partial pressure is one-fifth of the O 2 a 1 Δ g (υ 0) partial pressure. A simple chemical kinetics model demonstrates that measured O 2 a 1 Δ g pressures cannot be explained by gas-phase chemistry alone and must involve O atoms participating in surface reactions. It is found that collisional deactivation of O 2 a 1 Δ g on the tube walls must be included to satisfactorily model the experimentally observed pressures and trends. Modeling results also suggest that the O 2 a 1 Δ g surface production yield is 10% or more. Nomenclatureaverage thermal speed; 8RT∕πM p , m · s −1 γ = reaction efficiency χ = mole fraction Subscripts ac = absorption cell ave = average cal = calibration d = dissociation ep = endpoint ft = flow tube in = input J = rotational level N = atomic nitrogen NO = nitric oxide N2 = molecular nitrogen O = atomic oxygen O2= molecular oxygen O2Δ = singlet delta molecular oxygen O3 = ozone rc = resonance-enhanced multiphoton ionization cell tp = titration port υ = vibrational level w = wall

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Heterogeneous quenching of O₂(¹Delta_g) molecules in H₂:O₂mixtures

Cited by 31 publications

References 26 publications

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

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

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

Singlet Molecular Oxygen Formation by O-Atom Recombination on Fused-Quartz Surfaces

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Heterogeneous quenching of O2(1Deltag) molecules in H2:O2mixtures

Cited by 31 publications

References 26 publications

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

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

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

Singlet Molecular Oxygen Formation by O-Atom Recombination on Fused-Quartz Surfaces

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Heterogeneous quenching of O₂(¹Delta_g) molecules in H₂:O₂mixtures

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

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

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