Neutral gas composition

The analysis of the neutral gas composition in a discharge yields useful information on the mechanisms and kinetics of silane dissociation. However, it should be borne in mind that with mass-spectrometric analysis one only detects the final products of a possibly long chain of reactions. 

Any body in our solar system that has a surrounding neutral gas envelope, due either to gravitational attraction (e.g., planets) or some other processes such as sputtering (e.g., Europa) or sublimation (comets), also has an ionosphere. The very basic processes of ionization, chemical transformation, and diffusive as well as convective transport are analogous in all ionospheres the major differences are the result of the background neutral gas compositions, the nature or lack of a magnetic field, and the differences in some of the important processes (e.g., photo versus impact ionization). The remainder of this chapter describes the characteristics of the Venus ionosphere as a representative example of the so-called inner or terrestrial planets, the ionosphere of Jupiter as representative of the outer or major planets, and finally the ionosphere of Titan to represent one of the moons in our solar system. 

In a partially ionized gas there are two limiting situations, the state with zero degree of ionization, that is, a neutral gas, and the state of a fully ionized plasma. As a starting point we take the first state in which all particles are bound. We wish to find a suitable description of such a system of interacting composite particles (atoms) starting with the basic properties of the interacting elementary particles (e, p). 

The density and temperature distribution of interstellar matter, contrary to its elemental composition, is strongly inhomogeneous. At least three different phases exist (e.g. Tielens 2005) (i) extended low-density bubbles of hot ionized gas (hot interstellar medium or HIM, mass fraction 0.003, volume fraction 0.5), resulting from series of SN explosions in mass-rich stellar clusters (ii) cold and dense clouds of neutral gas (cold and neutral interstellar medium or CNM, mass fraction 0.3, volume fraction 0.01), resulting from sweeping up of warm gas and (iii) a warm, either ionized or neutral, medium in between (warm interstellar medium or WIM, mass fraction 0.5, volume fraction 0.5). The essential properties of the three phases are indicated in Fig. 2.4. The coolest and most massive of the clouds are the molecular clouds (MC, mass fraction 0.2, volume fraction 0.0005), a separate component, that are the places of star formation, where new stars are formed as stellar clusters with total masses between about 200 and several 106 M0. 

Eberhardt P. (1999) Comet Halley s gas composition and extended sources results from the neutral mass spectrometer on Giotto. Space Sci. Rev. 90, 45-52. 

The effect of various operating conditions on the recovery of the pulping chemicals and heat values in the case of a neutral sulfite semichemical (NSSC) spent liquor has been described recently (I). The thermodynamic equilibria and kinetics of gasification which seem to apply to this same set of experiments were discussed elsewhere (9). Gas compositions and yields examined in the latter study showed that under some of the operating conditions investigated, commercially significant quantities of ammonia and methanol synthesis gases could be produced from NSSC-type spent liquors. 

Nelson (1967) has presented data on the neutral lipid composition of the erythrocytes of several species, namely, the cow, dog, goat, horse, pig, rabbit, rat, and sheep. He determined the cholesterol content by three methods gas-liquid, thin-layer, and column chromatography, the last in conjunction with infrared spectrophotometry. The results obtained by the three methods were in good agreement. In erythrocytes of the cow, for example, cholesterol comprised 30.2, 28.4, and 27.9% of the total lipid extract by gas-liquid chromatography, infrared spectrometry, and thin-... 

The first part of this chapter is a brief presentation of the interactions encountered by an ion that is moving through a neutral gas under the influence of a weak electric field. This simplified treatment pertains mainly to the classic form of linear ion mobility spectrometers (IMSs) and aspiration IMS devices. The motion of ions in other ion mobility devices, like the differential mobility spectrometer (DMS) and traveling wave (TW) IMS is also discussed. In the second part of the chapter, the implications on ion behavior in these embodiments of IMSs are discussed. The effects of the experimental parameters temperature, drift gas composition, moisture level of the supporting atmosphere, and concentration of the analytes are described in Chapter 11. 

Homonuclear associative ionization reactions have also been observed in studies in which the ionic abundances in gas discharges are determined mass spectrometrically as functions of pressure, discharge current, and gas composition. Reaction identification is difficult in such studies because of the complexity of the multitude of excitation, ionization, neutralization, and radiative processes occurring simultaneously. Nevertheless homonuclear associative ionization reactions have been reported in dc discharges in helium, neon, 63-65) argon, 65-68) krypton, and xenon. Associative ionization reactions have also been reported in rf discharges in helium, argon, and xenon. ... 

Fig. 3.2.3. Time evolution of the neutral species density in the gas-phase of a streamer in an air DBD. After a brief transient due to streamer formation, the neutral gas-phase reaches a definite composition in about 0.1 ms and it is then dissipated by diffusion in a few ms.

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