Secondary Reactions in the Ion Chamber of a Mass Spectrometer

Abstract

A study has been made with a mass spectrometer of the ionization efficiencies of a number of gases, using an ion source incorporating an electron velocity selector. It is found that the shapes of the I.E. curves are affected by numerous instrumental factors. These have been examined, and the data lead to the following conclusions. Ions may be formed on the walls of the ionization source, at energies different from those corresponding to the ionized states of the free molecules. Charge transfer reactions may occur between these bound ions, and other neutral molecules on the walls. The surface ions may subsequently become detached, and are detected at the collector of the mass spectrometer. It is suggested that these ions formed by such processes may account for many of the spurious ``breaks'' often found in measured I.E. curves. The sharpness of the structure in the present curves indicates that the half‐width of the electron energy spread is of the order of 0.02 ev.