CO2 dissociation stimulated by vibrational excitation

The mechanism of CO2 dissociation stimulated by vibrational excitation in plasma (5-6), (5-7) has the following three essential qualitative advantages in energy efficiency with respect to alternative non-equilibrium plasma-chemical mechanisms of CO2 dissociation ... 

PHYSICAL KINETICS OF CO2 DISSOCIATION, STIMULATED BY VIBRATIONAL EXCITATION OF THE MOLECULES IN NON-EQUILIBRIUM PLASMA... 

Physical Kinetics of CO2 Dissociation, Stimulated by Vibrational Excitation... 

Characteristic Time Scales of CO2 Dissociation in Plasma Stimulated by Vibrational Excitation of the Molecules VT-Relaxation Time... 

The highest energy efficiency of CO2 dissociation in plasma can be achieved through its stimulation by vibrational excitation. This mechanism permits, in particular, 80% energy efficiency to be reached in non-thermal microwave discharges of moderate pressure (see Section 5.5.2). The main cause of energy losses in these systems is VT relaxation from low vibrational levels of CO2 molecules, which decreases exponentially with reduction of translational gas temperature. A significant decrease of translational gas temperatures (to... 

Similarly to the CO2 dissociation, a significant contribution of vibrational excitation in plasma-chemical H2O dissociation kinetics (Bochin et al., 1977, 1979) is due to the possibility of transfering most of the discharge energy there (more than 80% at 7 1 eV see Fig. 5-54, Givotov et al., 1981). The dissociation of H2O molecules in plasma, stimulated by vibrational excitation, follows three major kinetic steps ... 

Figure 5-56. Temperature restrictions for stability of the products of CO2 dissociation in plasma stimulated by vibrational excitation. Explosion and reverse reactions take place to the right and down from the curve stability is to the left and up.

Flow Velocity and Compressibility Effects on CO2 Vibrational Relaxation Kinetics. Analyze the characteristic VT -relaxation time (5-51) and the maximum linear preheating temperature (5-53) during CO2 dissociation in plasma stimulated by vibrational excitation, taking into account the gas compressibility. Describe the qualitative difference of the systems performed in subsonic flows (M 1), supersonic flows (M 1), and near the speed of sound. 

The formula can be applied in the case of IXeEaT /hcoTo < 1, where hco and Xe are the vibrational quantum and anharmonicity coefficient of N2 molecules. Compare the rate coefficient (6-34) for NO synthesis stimulated by vibrational excitation with that of CO2 dissociation (see Section 5.2). Because NO synthesis represents the slow reaction, the rate coefficient (6-34) includes detailed characteristics of the elementary process in contrast to the case of fast reaction in plasma-chemical CO2 dissociation. For calculations of the rate coefficient using equation (6-34) at typical non-equilibrium plasma conditions (T 3000 K, To < 1000 K), one can take the pre-exponential factor Ao = 10 -10 cm°/s. 

Let us analyze the energy balanee of CO2 dissociation stimulated in plasma by vibrational excitation in the two-temperature approximation, assuming one-dimentional gas motion with density p through the plasma in the x-direction with velocity u. Such an energy balance can be illustrated in the framework of the following equations describing major energy transfer, relaxation, and chemical reaction processes separately for different individual vibrational modes in the plasma-chemical system, which includes CO2 and products of its dissociation (Rusanov Fridman, 1984) ... 

Threshold Values of Vibrational Temperature, Specific Energy Input, and Ionization Degree for Effective Stimulation of CO2 Dissociation by Vibrational Excitation of the Molecules... 

The critical vibrational temperature corresponds to equality between the rates of vibrational excitationby electron impact and vibrational relaxation (see Chapter 3, and Section 5.3 for a similar case involving plasma-chemical CO2 dissociation). Stimulation of plasma-chemical processes by vibrational excitation becomes effective when The total... 

The most eneigy-efifective mechanism of NO synthesis in plasma is related to stimulation of the process under non-equilibrium conditions by vibrational excitation of N2 molecules. The kinetics of this process is controlled by the Zeldovich mechanism (see Section 6.1.2) and is limited by the elementary endothermic reaction (6-2) of a vibrationally excited N2 molecule. Thus, elementary reaction (6-2) plays a key role in the entire plasma-chemical NO synthesis. This elementary reaction is limited not by W relaxation and formation of molecules with sufficient energy (as in the case of CO2 dissociation see Section 5.3), but by the elementary process of the chemical reaction itself. That is why the elementary process (6-2) should be considered to describe the Zeldovich kinetics of NO synthesis in non-equilibrium plasma. 

The recent discovery of "multiphoton dissociation" of polyatomic molecules, where molecules, such as SFg, can be dissociated by multiple absorption of infrared laser photons, has stimulated many theoretical [14.13] and experimental [14.14] investigations about the mechanism of this process. Since the first steps, namely the excitation of lower vibrational levels with moderate level density may be isotope selective, the multiphoton dissociation may turn out to become a cheap and efficient way of laser isotope separation. Infrared lasers, such as the CO2 laser, have a high conversion efficiency which makes CO2 laser photons inexpensive. For more detailed discussions of the various aspects of laser isotope separation see [14.15-17]. 

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