Study of Carbon Monoxide, Nitrogen, Propylene, and Benzene Ionization Probability Curves near Threshold

Ionization probability curves for the formation of CO+, N2+, C3H6+, and C6H6+ have been obtained for some six volts above threshold. The technique employed provided both ionization by essentially monoenergetic electrons and a m/ε separation of the ions. In the case of the diatomic ions, the structure in the curves can be interpreted in terms of spectroscopically identified energy levels. The curves for propylene and benzene exhibit considerable structure which, when analyzed in a similar manner to that used for the diatomic molecules, results in the location of a number of unidentified energy levels. The presence of these levels explains the discrepancies in ionization potential measurements obtained by various electron impact methods.