Electron Attachment in Oxygen

Abstract

THE various collisional processes of electron attachment in electronegative gases are of interest in the examination of the properties of ionized gases not only in gas discharge tubes but also in the upper atmosphere, so that the data on attachment cross-sections are important. When the electric field E is high enough to produce ionization by electrons by collision, the attachment cross-sections cannot be measured by the direct methods possible at low electron energies. At high electron energies, however, the total cross-section can be calculated from data on the coefficient of attachment defined in a way analogous to that of α, the coefficient of primary ionization. The coefficient of attachment must be computed from measurements on the growth of ionization currents, preferably between parallel plates. In the presence of attachment the steady-state spatial growth of ionization in a uniform electric field at a constant value of E/p (p the gas pressure) can be represented by: where I is the amplified ionization current, at an electrode separation d, resulting from a small externally maintained current I₀(∼10⁻¹³ A), α′ is the apparent primary ionization coefficient, ω a generalized secondary ionization coefficient and a_t the total attachment coefficient representing the action of several possible attachment processes.