Kinetics plasma-chemical

Modelling plasma chemical systems is a complex task, because these system are far from thennodynamical equilibrium. A complete model includes the external electric circuit, the various physical volume and surface reactions, the space charges and the internal electric fields, the electron kinetics, the homogeneous chemical reactions in the plasma volume as well as the heterogeneous reactions at the walls or electrodes. These reactions are initiated primarily by the electrons. In most cases, plasma chemical reactors work with a flowing gas so that the flow conditions, laminar or turbulent, must be taken into account. As discussed before, the electron gas is not in thennodynamic equilibrium... 

The concept of macroscopic kinetics avoids the difficulties of microscopic kinetics [46, 47] This method allows a very compact description of different non-thennal plasma chemical reactors working with continuous gas flows or closed reactor systems. The state of the plasma chemical reaction is investigated, not in the active plasma zone, but... 

Ions are charged heavy particles, that are able to make a sigiuficant contribution to plasma-chemical kinetics either due to their high energy (as in the case of sputtering and reactive ion etching) or due to their ability to suppress activation barriers of chemical reactions. This second feature of plasma ions results in the so-called ion or plasma catalysis, which is particularly essential in plasma-assisted ignition and flame stabilization, fuel... 

Plasma is not only a multi-component system, but often a very non-equihbrium one (see Section 1.3). Concentrations of the active species described earlier can exceed those of quasi-equilibrium systems by maiy orders of magnitude at the same gas temperature. The successful control of plasma permits chemical processes to be directed in a desired direction, selectively, and through an optimal mechanism. Control of a plasma-chemical system requires detailed understanding of elementary processes and the kinetics of the chemically active plasma. The major fundamentals of plasma physics, elementary processes in plasma, and plasma kinetics are to be discussed in Chapters 2 and 3 more details on the subject can be found in Fridman and Keimedy (2004). 

Positive ions are obvionsly major players in plasma-chemical processes. Their exothermic reactions with neutrals usually have no activation energy, which makes their contribution significant in many specific plasma-chemical processes, particularly in plasma catalysis. In addition to high chemical activity, the ions can have significant kinetic eneigy, which determines their contribntion, for example, in reactive ion etching. 

The kinetics of plasma-chemical reactions of vibrationally excited molecnles is determined not only by their concentration but mostly by the fraction of highly excited molecnles able to dissociate or participate in endothermic chemical reactions. The formation of highly vibrationally excited molecules at elevated pressures is due not to direct electron impact but to collisional energy exchange called W relaxation. Most conventional resonant W processes usually imply vibrational energy exchange between molecules of the same kind, for example, N2(w = 1) + N2(w = 0) N2(w = 0) - - = 1), and are char-... 

The high rates of plasma-chemical reactions are often due to a high concentration of excited atoms and molecules in electric discharges. Vibrational and electronic excitations play the most important role in the stimulation of endothermic processes in plasma. We next focus on reactions of vibrationally excited molecules, which are easier to analyze. The kinetic relations, however, can also be applied to some extent to reactions of electronically excited particles. 

Plasma-chemical reaction rates depend on the probability of relevant elementary processes from a fixed quantum-mechaiucal state with fixed energy, which was considered in the previons chapter, and the nnmber density of particles with this energy and in this particular qnantnm-mechanical state, which is to be considered in this chapter. A straightforward determination of the particles distribution in plasma over different energies and different quantum-mechaitical states is related to detailed physical kinetics (see Fridman Keimedy,... 

However, wherever possible, the application of quasi-equilibrium statistical distributions is the easiest and clearest way to describe the kinetics and thermodynantics of plasma-chemical systems. 

A detailed description of non-equilibrium plasma-chemical systems and processes generally requires an application of kinetic models. The application of statistical models leads sometimes to significant errors (Slovetsky, 1980). In some specific systems, however, statistical approaches can be not only simple but also quite successful in describing non-equilibrium plasma, which is discussed next. 

Plasma-Chemical Kinetics, Thermodynamics, and Electrodynamics Table 3-2. Coefficients of Free Diffusion of Electrons and Ions at Room Temperature... 

Vibrationally and electronically excited atoms and molecules, which make a significant contribution to plasma-chemical kinetics, can be described in terms of distribution functions. We already introduced the vibrational distribution functions (population of vibrationally... 

Reverse Isotopic Effect in Plasma-Chemical Kinetics... 

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