Excitation Processes in the Hollow Cathode Discharge

Abstract

The low potential gradients in the negative glow in a hollow cathode discharge in a rare gas make it a favorable source for the excitation of metallic spark spectra. The metal studied forms the cathode, and is brought into the discharge by cathode sputtering or evaporation. The excitation is limited by collisions of the second kind between gas and metal atoms and ions. The spectroscopic data of all the available cases have been examined to see what determines the processes occurring. In general only those processes occur in which the metal can be excited to some term in the spark spectrum with gain or loss of only a small amount of kinetic energy to balance the reaction equation. High melting point metals or those which sputter poorly cathodically enter the discharge in helium in the normal state or in a low metastable state of the atom. With low boiling points metals appreciable numbers of metal ions enter the reactions. In intermediate cases or in argon or neon, it is not always possible to predict if metal ions will enter the reaction or not. The conditions which determine the results are discussed.