The calibration of the electron energy scale for ionization potential measurements

Abstract

The theoretically evaluated electron energy distribution curve from a function of the type U exp ( - U/kT), as given by Fowler and Honig, for electrons emitted from a heated filament is compared with the experimentally determined curve. The shift in the maxima of the experimental curve as compared with the theoretical one is attributed to the contact potential in the system, and consequently this shift has been used as a means of evaluating the contact potential during the course of an experiment. The shape of the ionization efficiency curve is analysed and the linearly extrapolated value is shown to be lower than the true ionization potential by 2 kT when the ionizing electrons have a distribution corresponding to the above mentioned function. Finally the experimentally determined contact potential and the value 2 kT evaluated corresponding to the filament temperature are used to obtain the ionization potentials in four gases on an absolute scale to within ±0.08 ev. The results are compared with spectroscopic data.