Flowing afterglow density

Figure 7. Schematic diagram of a flowing-afterglow electron-ion experiment. The diameter of flow tubes is typically 5 to 10 cm and the length is 1 to 2 meters. The carrier gas (helium) enters through the discharge and flows with a velocity of 50 to 100 m/s towards the downstream end of the tube where it exits into a fast pump. Recombination occurs mainly in the region 10 to 20 cm downstream from the movable reagent inlet, at which the ions under study are produced by ion-molecule reactions. The Langmuir probe measures the variation of the electron density in that region. A differentially pumped mass spectrometer is used to determine which ion species are present in the plasma.

McNeil, Lai and Murad ° have used the cross sections of Levandier et al. in models for the calculation of permanent sodium and sodium ion metal layers. Figure 16 compares the nighttime altitude density profiles of sodium and sodium ion calculated using the thermal flowing afterglow measurements of Farragher et al. and the cross sections of Levandier et including thermal extrapolations of the respective data. The... 

Radiative Association Reactions The study of radiative association reactions, (Eq. 2.2), has been of considerable interest [6-8] in chemical kinetics, planetary and interstellar chemistry, flames, and a variety of other areas. The kinetic study makes it possible to model the formation of complex molecular species in the interstellar science. At the very low molecular number densities in interstellar environments, the probability of formation of the products of association reactions by collisional stabilization is very low. Therefore, the radiative association process becomes an extremely important one for the production of the complex molecular species observed by astronomical physicist. The methodology is either flowing afterglow (FA) or Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. For the study of the apparent bimolecular rate constant for formation of association products as a function of pressme of a third body (N), the pressure should be set up to be sufficiently high in order to release the energy in the associated complex. Under the high pressure conditions collisional stabilization has competed with and usually dominated over radiative associatioiL As a result, the radiative association rate was then extrapolated from the intercept of a plot of apparent rate constant versus pressure of a third body, N. 

All afterglow experiments, whether the plasma is stationary or flowing, have in common that the recombination occurs in the presence of a substantial density of third particles, such as neutral atoms, electrons, and ions. One measures the volume loss rate of free electrons and derives a deionization coefficient, ... 

Flow through plasma then afterglow CO oxidation C02 dissociation Axial plug flow Mean electron density and energy 68... 

Tubular reactor with afterglow CF4 etching Si Plug flow Assumed mean density and energy in discharge 76... 

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