| Summary: | The presence of a retarding potential in a space charge limited diode is used to obtain the effect of an essentially monoenergetic electron beam by the R. P. D. method. The performance of an ion source, using this electron gun, is treated theoretically and tested experimentally with argon. Further tests on Xe+, N2+ and SF6- ions serves to illustrate the effectiveness of this ion source. An electron impact study of nitric oxide was made using this ion source. The ionization potential of NO was found to be 9.25 ±. 02 eV., and the ionization efficiency curve for NO+ to be non-linear near the onset. This curvature is interpreted in terms of ionization to various vibrational states of the NO+ ions. Appearance potentials were obtained for the formation of N+, O+ and O- ions from a number of processes.
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