Studies of Ionization Efficiency. I. The Determination of Molecular Appearance Potentials Using the Mass Spectrometer

Abstract

The factors affecting the shape of ionization efficiency curves can be separated into two categories: those due to instrument design, and those depending on the molecular structure of the substance studied. By taking precautions to eliminate the former, details of individual fine structure can be detected and measured in the curves. The methods for the determination of appearance potentials in use at the present time are discussed, and the results for a number of substances measured by the principal methods are compared with spectroscopic ionization potentials. It is found that the critical slope method gives values in all cases within 0.3 volt of the spectroscopic figure, whereas the results of the other methods may be in error.