Electron Ionization Frequency in Hydrogen

The frequency of ionization by electrons in hydrogen has been measured during pulsed microwave breakdown in a waveguide. Optical radiation emanating from the plasma was used to determine the temporal rate of growth of electron density. Values of the ionization frequency are presented as a function of Eₑp₀ for 36<Eₑp₀<200 V/cm-mm Hg. The measurements constitute an extension of the work of Madan, Gordon, Buchsbaum, and Brown who measured this coefficient up to an Eₑp₀ of 40 V/cm-mm Hg by microwave cavity techniques. Comparison is made with previous dc measurements of Rose and with the theory of Allis and Brown. Good agreement is obtained with the measurements of Rose but not with the theory of Allis and Brown extended to high Eₑp₀, nor with the previous microwave measurements of Madan et al.