Ionization efficiency curves obtained by the RPD (retarding potential difference) method are presented for Cycl. C 4 F 8 − , H g + , C 2 H 2 + and C 2 F 4 + . The C 4 F 8 − resonance capture curve is given for a variety of experimental conditions. The curves for the positive ions are compared with similar curves obtained previously by the technique of photoionization combined with mass analysis. The results are discussed in terms of possible relaxation effects and other artefacts in the RPD method and in terms of threshold laws of ionization by electron and photon impact. Special emphasis is placed on autoionization processes. Experimental conditions, under which the RPD ion source may be reliably used, are specified.
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Grajower et al. (1968) studied this question.