Electron Attachment and Negative Ion Formation in Oxygen and Oxygen Mixtures

Abstract

A direct method is employed to determine the probability of electron capture in oxygen and oxygen mixtures. The principle of the method lies in the analysis of a mixed current stream at two points along its path by means of wire grids which permit only the ionic fraction of the current to pass when a high frequency field is applied between adjacent grid wires. A means of measuring the mobility of the electrons is also possible. The probability of attachment has been determined for oxygen, air, and mixtures of oxygen with the rare gases. The probability of attachment is a marked function of the electronic energy, decreasing with increase in electronic energy. In oxygen and in all mixtures of oxygen, however, there is an increase in the probability of attachment occurring at approximately 1.6 volts electronic energy. This can be definitely explained as being due to the appearance of low energy electrons following inelastic impacts with ${\mathrm{O}}_2$ molecules. The energy at which these inelastic impacts begin is well correlated with the first excited level of the ${\mathrm{O}}_2$ molecules which is 1.62 volts above the ground state.