ELECTRON-TEMPERATURE DEPENDENCE OF ELECTRON-ION RECOMBINATION IN ARGON

A 3-mode microwave apparatus is used to study the dependence of the dissociative recombination coefficient α(Ar2+) on electron temperature Te over the range 300aK<e< 10 000aK while the ion and gas temperatures remain at 300A°K. A high-Q cavity mode is used to ionize the gas periodically, a second high-Q mode is used to determine the decay of electron density during the afterglow from the change of resonant frequency of the cavity, and a nonresonant waveguide mode is used to apply a constant microwave heating field to the electrons. At Te=300a K, a value α(Ar2+)=(8.5±0.8)×10- 7 cm3/sec is obtained from analysis of recombination-controlled electron-density decays using a computer solution of the electron continuity equation which includes recombination and ambipolar diffusion terms. Over the range 300aK<~Te<~10 000aK, the coefficient α(Ar2+) is found to follow a simple Te-0.67 variation. This result is reconciled with Fox and Hobson's T-1.3 variation, obtained under conditions where Te=Ti=T, on the basis of their changing Ar2+ vibrational-state populations with changing temperature. Finally, it is noted that our Te-0.67 variation may be evidence for appreciable electron capture via the indirect as well as the direct dissociative process. © 1968 The American Physical Society.