Abstract
During the course of a mass spectrometric study of thermal negative chloride ion production from hydrogen chloride molecules incident upon a tungsten filament (F) at a high temperature (2, 000-2, 200K), we found an abnormal emission of a negative ion, which changed in mass position in a mass spectrum according to a change in the ion-extraction voltage applied to F and which was stronger in emission current than the thermal chloride ion emitted from F. Possible mechanisms of secondary negative ion production by a very strong thermal electron emission current (>10 mA) were examined from the viewpoint of kinetic energy of the ion under study. Results thus obtained lead to the conclusion that the abnormal ion of interest is the secondary negative chloride ion desorbed by electron impact on the inside surface of a stainless steel cylinder surrounding F and also suggest that the present phenomenon of electron-stimulated negative ion desorption from a surface at a very low temperature (less than about 600K) may provide a strong and stable negative ion source available for even those atoms and radicals with a smaller value of electron affinity.
