PERIODIC NATURE OF METAL-NOBLE GAS ADDUCT IONS IN GLOW-DISCHARGE MASS-SPECTROMETRY

The observation that ZnAr+ ion currents in a glow discharge can measur e as high as 30% of those of Zn+ prompted a systematic study of metal- noble gas diatomic species. Twenty-four elements in combination with n eon, argon, and krypton were included. Periodicity of behavior was obs erved from one row to the next with all three noble gases; periodicity was also observed as the identity of the noble gas was changed. The d iatomic noble gas adduct ions of zinc, cadmium, and mercury (group 12) each displayed a concentration relative to the corresponding metal io n that was well above that of other elements in their respective rows. Investigation of the cause of this phenomenon eliminated glow dischar ge pressure and power conditions. Binding energies of the various spec ies were qualitatively consistent with the observation of relative abu ndances of metal-noble gas diatomic ions as they varied with the ident ity of the noble gas, but did not explain why ZnX(+), CdX(+), and HgX( +) form in what seem to be anomalously high abundance. Variations in t he sputtering rates of the transition metals (Zn > Cu > Ni > Fe) are c onsistent with the observation that ZnX(+) > CuX(+) > NIX(+) > FeX(+); the resulting increase in collision frequency (with increasing sputte ring rate) is believed to account for the relative abundances of these adduct ions in the discharge.