Measurement of Ionization Potentials by Electron Impact

Abstract

A comparison has been made between the different methods of extracting ionization potentials from ionization efficiency curves measured by electron impact. Conventional methods are usually accurate to ±0.1 ev but the assumptions on which they are based are such that no further increase in accuracy can be expected. These methods sometimes give wildly inaccurate results; the main cause of this is the presence of fine structure in the ionization efficiency curve. Morrison's method of determining ionization potentials, because it detects fine structure, enables measurements accurate to ±0.02 ev to be made. Other methods which detect fine structure are equally accurate but require more complex apparatus.