Infrared diode laser spectroscopy has been used as a diagnostic probe to measure the concentrations of the methyl radical and stable products in an ac methane/hydrogen/oxygen (CH4−H2−O2) plasma. Among the products detected were all of the stable C-2 hydrocarbons and oxygen-containing species including methanol, formaldehyde, formic acid, carbon monoxide, and carbon dioxide. A simple one-dimensional chemical modeling program has been written to calculate and compare the model concentrations of all the detected species with their observed concentrations. Good agreement between these values has been obtained which enables some insights to be gained into the gas-phase mechanism in mixed methane plasmas.
An apparatus is described which samples and analyzes ions from a glow discharge. Results are given for the positive column of discharges in argon, krypton, and mixtures of the two, at pressures between 0.4 and 1.0 mm and current densities in the range 0.035 to 0.105 ma/cm 2 • In general, the results are in reasonable agreement with those of other workers, but some differences are noted.The results appear to favor the formation of A2+ by the reaction Ar*+Ar-+A 2 ++e, but it is not possible to rule out conclUSively the three-body process Ar++2Ar-+Ar2++Ar. Traces of hydrogenous impurities (especially water) appear to interfere with molecule ion formation.The formation of ArH+ from impurities is also studied and the results suggest that it may be formed from any or all of Ar+, Ar2+ or Ar*. Experiments in which 1.25% hydrogen is added to the argon suggest that ArH+ is not formed mainly by the reaction of Ar+ with H2 but that the reaction of metastable argon atoms with hydrogen atoms should be seriously considered.The visible structure of a striated positive column is found to be reflected in the ion concentrations which vary differently for different ions. The effect seems to be related to fluctuations in the potential gradient which may be enhanced by the formation of negative ions. 18 D. Barbiere, Phys. Rev. 84, 653 (1951).
The ions in the negative glow were examined at pressures of about 0.4 mm and currents of about 0.2 ma. Most of the work was done with argon but some measurements were made with helium and with helium-argon and argon-krypton mixtures. To clarify the role of impurities, some work was done with the addition of 1.25% hydrogen to the argon. The results confirm that the ions of the principal gas or gases are produced by the impact of ``primary'' electrons. Evidence is obtained that when small amounts of gases having sufficiently low ionization potentials are present, they are ionized by interaction with the metastable atoms of the principal gas. Ar2+ appears to form in the negative glow mainly by Ar++2Ar→Ar2++Ar,but it is confirmed that in the positive column a process depending mainly on excitation must be dominant. The formation of ArH+ from impurities is thought to occur principally by the reaction of metastable argon atoms with hydrogen atoms, the latter being produced from various sources by electron impact. In the presence of appreciable quantities of hydrogen, the reactionAr++H2→ArH++Happears to contribute but is only important at the cathode edge of the negative glow. The extremely persistent formation of H3O+ from traces of water suggests that long-lived excited states of water may exist, and be responsible for this effect.
Ions in the negative glow and positive column of a dc glow discharge in nitrogen have been examined at a pressure of 0.4 mm and a current density of 0.03 mA/cm2. Mixtures of nitrogen with hydrogen (0.9%) and with oxygen (0.5% and 20%) were also used. In addition to N2+ and N+, the ions N3+ and N4+ are prominent in the negative glow in pure nitrogen. They appear to be formed by N++2N2→N3++N2, N2++2N2→N4++N2, both of which proceed to an extent dependent on field strength. With added hydrogen the ions N2H+ and NH4+ become important. N2H+ appears to be formed by at least two processes. The concentration of NH4+ is greatest in the tail of the negative glow where vibrational excitation is a possible factor and the residence time of ions is relatively long. In the presence of oxygen the ions NO2+ and N2O+ appear, as well as O2+, but the most prominent oxygen-containing ion is NO+. The mechanism of formation of these ions is not definitely assigned but charge-transfer reactions may be important, as well as ion-molecule reactions which depend to some extent upon vibrational excitation, or upon residence time in the discharge.
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