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The rate of the chemical reaction Xe+Xe++e-between 4200-7600°K has been followed by microwave absorption in a shock tube. Results are explained in terms of the mechanism : M+XezM+Xe*+M+Xe++e-.The complex rates are resolved into two empirical rate constants, kl and k2. From the observed activation energies it is concluded that b g c , and in this case the empirical kl is a and the empirical k:! is c. The activation energies are : El = 8-4& 1 eV, and E2 = 3.7fl eV (the ionization potential of xenon is 12.1 eV), and the cross-section for the second process is about 103 times that for the first. By virtue of imprisonment of resonance radiation, the quantum of energy represented by Xe* is held in the system for a large number of collisions.

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The rate and mechanism of the thermal ionization of xenon has been further studied by a microwave and shock-tube method. The negligible effect of impurities or background on the observed ionization rates was demonstrated. For a variety of added gases, the activation energy for the observed ionization was about 8 eV, not 12.1 eV, the ionization energy. Detailed time studies show an induction period for buildup of free electrons as a result of populating intermediate electronic states of xenon; however, the simple three-step mechanism proposed previously (Xe+M⇋Xe*+M,Xe*+M→Xe++e−+M) was shown to be insufficient to explain certain quantitative features of the data. At these high temperatures a large number of parallel paths are possible, and in general, entropy differences are more important than energy differences. On this basis it is argued that the final ionization process leads to Xe++e—+M and not MXe++e—. Limited data are presented on the ionization of krypton, and an activation energy of about 10 eV, not 14 eV (the ionization energy), is indicated. Reaction cross sections are given for xenon and krypton.

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