Measurement of Excitation ofN2, CO, and He by Electron Impact

Abstract

The inelastic excitation of ${\mathrm{N}}_2$ and CO by electron impact is studied using the trapped-electron method. In this method those electrons which have lost a portion of their initial energy in an inelastic collision are trapped in a potential well. Well depths up to 3 volts are used in the present experiment. The operation of the apparatus is checked for helium, where the shape of the excitation function is known accurately. The shape of the excitation function for metastable helium atoms obtained by the trapped-electron method is in good agreement with previous results. A large inelastic peak is observed at 2.3 ev in ${\mathrm{N}}_2$ and 1.7 ev in CO. This phenomenon is discussed in terms of the formation of a temporary negative ion state of ${\mathrm{N}}_2$ or CO and subsequent decay into various vibrational levels of the molecule. This model explains the sharp peak in both the elastic and inelastic cross section in ${\mathrm{N}}_2$ and CO. Neither ${\mathrm{O}}_2$ nor ${\mathrm{H}}_2$ show such a sharp peak at low energies.