Contribution of singly and doubly ionized argon to the autoionization (Auger) spectrum of argon excited by bombardment of magnesium and scandium surfaces

Electron spectra provided by bombarding targets of Mg and Sc using argon io ns accelerated through potentials between 300 V and 5 kV are reported for d ifferent electron energies in the ionizer box of a hot filament type ion gu n. By suitable choice of ionizer energy, beams of Ar+ and beams of mixed Ar + and Ar2+ ions could be produced. It is shown that Ar+ and Ar2+ ions can b oth give rise to similar argon Auger spectra but the behaviour of the inten sities of the Auger peaks differs with the ionic species. In the case of ex citation by Ar+ ions no spectrum is visible below a threshold energy (280 e V for Sc, 2.8 keV for Mg) but beyond threshold the size of the Augar peak i ncreases with ion energy. With Ar2+ excitation no threshold was observed do wn to the lowest accelerating potential used and the Augar signal was found to decrease with increase in ion energy. This behaviour is consistent with two different mechanisms being responsible for the Ar** state which initia tes the autoionization process.