Gases, chemical equilibrium electrically excited

Thus, for electrical sources in thermal equilibrium, the processes of dissociation, excitation, and ionization can be treated as if the gas mixture were contained in a furnace at the same temperature. Excitation is described by the Maxwell-Boltz-mann distribution law (Eqn. 10.2), ionization by the Saha relationship (Eqn. 11.1), and dissociation by the general relationships for chemical equilibrium. 

When an electric discharge is passed through a cold diatomic gas at low pressure it is partially dissociated into atoms in this way reasonable concentrations of O, H, D, N, halogen or other atoms can be produced in a chemically inert diluent. The recombination of these atoms, and their reaction with other molecules can be observed as the gas flows down a long tube. Many of the reactions produce molecules in excited electronic states the resulting chemiluminescence can be used to measure the concentration of atomic species as a function of distance, and hence time, down the tube. Dr Clyne describes this important technique, which has produced direct measurements of the rates of many exothermic reactions of atoms and free radicals at room temperature and below. The reverse of the recombination steps are, of course, the dissociation reactions whose kinetics at high temperatures were described in the first chapter if the ratio of forward and reverse rate constants is equal to the equilibrium constant, the temperature dependence of these rates can be deduced over very wide ranges of temperature. 

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