Ion clusters in He–Co and Ar–Co glow discharges

Kaufman, Y.; Avivi, P.; Dothan, F.; Keren, Hila; Malinowitz, J.

doi:10.1063/1.439459

Cited by 25 publications

(14 citation statements)

References 10 publications

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“…Practically, the vapor phase C 2 molecule and the ion clusters of the general form (CO) 2 C + m (m=1-15) are known to form as intermediates in CO plasma. 11,17) Our oxygen/carbon ratio agrees approximately with those reported by Maksimov et al 18) They have reported that oxygen/carbon mole ratio in the carbon film formed in CO glow discharge is O/C∼0.5 although their discharge current 30 mA is higher than that of our experiments.…”

Section: Reaction Products and Empirical Formulasupporting

confidence: 62%

Carbon and Oxygen Isotope Separation by Plasma Chemical Reactions in Carbon Monoxide Glow Discharge

Mori

Akatsuka

Suzuki

2001

Journal of Nuclear Science and Technology

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The separation of carbon and oxygen isotopes in CO glow discharge has been studied. The isotope enrichment in the products was measured by quadru-pole mass spectrometer. The reaction yield and empirical formula of solid phase products were determined by the gas-volumetric analysis. The stable products obtained in our experiment are CO 2 and solid polymers formed on the discharge wall. The polymer consists of both carbon and oxygen and the oxygen/carbon mole ratio in the polymer is 0.35±0.05. The isotope enrichment coefficients show a strong negative dependence on discharge current though the relative reaction yields have an opposite tendency. Consequently, the maximum isotope enrichment coefficients for 13 C in wall deposit of 2.31 and for 18 O in CO 2 of 1.37 are obtained when the discharge current and the reaction yields are minimum in our experimental range. The experimental results of isotope enrichment have been compared with theoretical values estimated by an analytical model of literature. The dilution mechanism of the isotope enrichment of stable products is inferred from the isotopic distributions of 13 C and 18 O in products and theoretical predictions for isotope enrichment.

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Section: Reaction Products and Empirical Formulasupporting

confidence: 62%

Carbon and Oxygen Isotope Separation by Plasma Chemical Reactions in Carbon Monoxide Glow Discharge

Mori

Akatsuka

Suzuki

2001

Journal of Nuclear Science and Technology

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“…These results indicate the presence of large ion clusters in the CO/Ar plasma, which are apparently destroyed by adding small amounts of O 2 and NO. Such clusters, having the general form (CO) 2 C n , n = 1-15, have been previously observed in glow discharges in CO/Ar and CO/He mixtures [26]. In addition, a mass spectrum of the electrode deposit shows a number of peaks above 100 amu [25] (see figure 12).…”

Section: Thomson Discharge Measurementssupporting

confidence: 59%

Ionization measurements in optically pumped discharges

Plönjes

Palm

Adamovich

et al. 2000

J. Phys. D: Appl. Phys.

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The kinetics of ionization and electron removal in optically pumped non-equilibrium plasmas sustained by a CO laser are studied using non-self-sustained dc and RF electric discharges. Experiments in optically pumped CO/Ar/N2 mixtures doped with O2 and NO demonstrated that associative ionization of CO produces free electrons at a rate up to S = 1015 cm-3 s-1. The ionization rate coefficient, inferred from the CO vibrational population measurements, is kion = (1.1-1.8)×10-13 cm3 s-1. It is shown that excited NO and possibly O2 molecules also contribute to the vibrationally stimulated ionization process. In a CO/Ar plasma, applying a dc bias to the cell electrodes resulted in the rapid accumulation of a deposit on the negative electrode due to a large cluster ion current. The average mass of an ion in this plasma, estimated by measuring the mass of the deposit, is m≅250 amu, which is consistent with the mass spectrometer analysis of the deposit. The deposit did not accumulate when small amounts of O2 and NO were added to the CO/Ar plasma, which presumably indicates the destruction of the cluster ions. It is demonstrated that adding small amounts of O2 to the optically pumped CO/Ar plasmas significantly increases the electron density, from ne = (4-7)×109 cm-3 to ne = (1-2)×1011 cm-3. This effect occurs at a nearly constant (within 50%) electron production rate S, indicating a substantial reduction in the overall electron removal rate. This reduction can be qualitatively interpreted as the destruction of rapidly recombining cluster ions in the presence of the O2 additive, and their replacement by monomer ions with a slower recombination rate. Further studies of the ion composition in optically pumped plasmas are suggested.

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“…In the present work the electron density with the rf field turned off and on has not been measured. Electron density measurements using both microwave attenuation 12 and filtered Thomson scattering, as well as ion composition measurements using in situ ion mass spectrometry, 24,25 would provide additional insight into the kinetics of these unique high-pressure nonequilibrium plasmas.…”

Section: Resultsmentioning

confidence: 99%

“…This result is consistent with previous measurements of the ion composition in glow discharges in CO-Ar-O 2 and CO-He-O 2 mixtures. 24,25 These previous studies showed that in a discharge in CO-Ar and CO-He mixtures without oxygen the dominant ions are rapidly recombining cluster ions such as C n (CO) 2 ϩ , n ϭ1 -12. However, adding a few tens of mTorr of O 2 resulted in a nearly complete destruction of the cluster ions and their replacement by the slowly recombining monomer O 2 ϩ ions.…”

Section: Methodsmentioning

confidence: 98%

Radio frequency energy coupling to high-pressure optically pumped nonequilibrium plasmas

Plönjes

Palm

Lee

et al. 2001

Journal of Applied Physics

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This article presents an experimental demonstration of a high-pressure unconditionally stable nonequilibrium molecular plasma sustained by a combination of a continuous wave CO laser and a sub-breakdown radio frequency ͑rf͒ electric field. The plasma is sustained in a CO/N 2 mixture containing trace amounts of NO or O 2 at pressures of Pϭ0.4-1.2 atm. The initial ionization of the gases is produced by an associative ionization mechanism in collisions of two CO molecules excited to high vibrational levels by resonance absorption of the CO laser radiation with subsequent vibration-vibration (V-V) pumping. Further vibrational excitation of both CO and N 2 is produced by free electrons heated by the applied rf field, which in turn produces additional ionization of these species by the associative ionization mechanism. In the present experiments, the reduced electric field, E/N, is sufficiently low to preclude field-induced electron impact ionization. Unconditional stability of the resultant cold molecular plasma is enabled by the negative feedback between gas heating and the associative ionization rate. Trace amounts of nitric oxide or oxygen added to the baseline CO/N 2 gas mixture considerably reduce the electron-ion dissociative recombination rate and thereby significantly increase the initial electron density. This allows triggering of the rf power coupling to the vibrational energy modes of the gas mixture. Vibrational level populations of CO and N 2 are monitored by infrared emission spectroscopy and spontaneous Raman spectroscopy. The experiments demonstrate that the use of a sub-breakdown rf field in addition to the CO laser allows an increase of the plasma volume by about an order of magnitude. Also, CO infrared emission spectra show that with the rf voltage turned on the number of vibrationally excited CO molecules along the line of sight increase by a factor of 3-7. Finally, spontaneous Raman spectra of N 2 show that with the rf voltage the vibrational temperature of nitrogen increases by up to 30%. This novel energy efficient approach allows sustaining large-volume high-pressure molecular plasmas without the use of a high-power CO laser. This opens a possibility of using the present technique for high-yield plasma chemical synthesis and plasma material processing.

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Ion clusters in He–Co and Ar–Co glow discharges

Cited by 25 publications

References 10 publications

Carbon and Oxygen Isotope Separation by Plasma Chemical Reactions in Carbon Monoxide Glow Discharge

Carbon and Oxygen Isotope Separation by Plasma Chemical Reactions in Carbon Monoxide Glow Discharge

Ionization measurements in optically pumped discharges

Radio frequency energy coupling to high-pressure optically pumped nonequilibrium plasmas

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