Energy Efficiency of Plasma-Chemical Processes Stimulated by Electronic Excitation and Dissociative Attachment

Energy Efficiency of Plasma-Chemical Processes Stimulated by Electronic Excitation and Dissociative Attachment 

Mechanisms of stimulation of plasma-chemical reactions by electronic excitation were discussed in Section 2.5.5. No one of the four kinetic factors mentioned in Section 3.6.2 can be apphed in this case therefore, energy efficiency is relatively low, usually below 20-30%. Plasma-chemical processes through electronic excitation can be energy effective if they initiate chain reactiorrs. Such a situation takes place, for example, in NO synthesis, where the Zeldovich mechanism can be effectively initiated by dissociation of molecular oxygen through electronic excitation (see Section 6.1.2). 

The plasma-chemical process that is based on dissociative attachment can become energy effective only if the same electron is able to participate in a reaction many times. In such a chain reaction, the detachment and liberation of the electron from a negative ion should be faster than the loss of the charged particle in ion-ion recombination. Water vapor dissociation in non-thermal plasma is an example of such a chain process. This plasma-chemical reaction is to be considered in detail in Sections 5.8.4 and 5.8.5. The energy efficiency of the chain process for this reaction can be relatively high 40-50%. 

The vibrational energy balance in a plasma-chemical process can be illnstrated by the following simplified one-component equation taking into account vibrational excitation by electron impact, VT relaxation, and chemical reaction (Rnsanov Fridman, 1984 Fridman Kennedy, 2004)  

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