Metastable metal ion production in sputtering dc glow discharge plasmas: Characterization by electronic state chromatography

The sputtering de glow discharge is a stable and intense source of a wide v ariety of metal ions for use in ion/molecule studies. We have examined fact ors influencing the formation of metastable excited states of sputtered spe cies in this device using the electronic state chromatography (ESC) techniq ue. These determinations are essential if the glow discharge is to be used as a source of metal ions for subsequent reaction, since the electronic con figuration of the metal can dramatically affect its reactivity in the gas p hase. Further, the ability to manipulate excited-state production provides the means for the study of state-specific behavior of these species. We hav e obtained evidence in a series of experiments that indicates that the glow discharge is capable of producing several metal ions in metastable excited states as well as the ground state. Identification of specific configurati ons for several first-, second-, and third-row metal ions has been made on the basis of reduced zero-field mobilities in He. Results suggest that sign ificant population of excited states higher than approximately 3.4 eV above the ion ground state does not occur in an Ar discharge for the metals exam ined here. Examination of the dependence of configuration distributions for several metal ions has revealed that excited-state production is sensitive to certain discharge parameters including pressure, distance to sampling o rifice, and working gas composition. These results suggest that production of excited metal ions in the discharge involves energetic electrons. Furthe r, some degree of deactivation of excited states occurs prior to extraction for ions whose excited states are collisionally coupled to lower states vi a interaction with the discharge gas. Metastable deactivation is enhanced i n the third-row ions as a result of large spin-orbit effects.