A Second Ionization Potential in Potassium Vapor

Abstract

The occurrence of a second peak in the photoionization curve of potassium vapor (Lawrence and Edlefsen) suggests that there might be a related peak (or discontinuity) in the curve for ionization by electron impact. The ionization in potassium vapor was investigated by Hertz' method of neutralization of space charge by positive ions. It was found that there was an abrupt increase in gradient of the ionization curve, indicating a second ionization potential at 0.97±0.05 volt above the first one corresponding to the series limit. With mercury vapor, the apparatus indicated the presence of Lawrence's ultraionization potentials in mercury vapor, together with three new ones (10.40, 10.62, 10.88, 11.28, 11.40, 11.77, 12.16, 12.46).