Electron impact ionization of gallium ions

Electron impact ionization cross sections sigma(q,q+n) for gallium ions hav e been measured for the reaction of Gaq+ --> Ga(((q+n)+))+ + (n+l)e for sin gle (n = 1, q = 1, 3, 8) and triple (n = 3, q = 3, 4) ionization. The measu rements have been performed using the crossed-beams technique in an energy range from the respective ionization threshold up to 1 keV; partly up to 6 keV. The cross sections for single ionization of ions in the charge state 9 = 1 and 3 show contributions below the ground state threshold caused by ionizat ion of ions in excited, long-lived states in the parent ion beam. The cross sections are compared with the semiempirical Lotz formula. The cross section for Ga4+ triple ionization shows contributions from inner -shell processes. Semiempirical formulae are in good agreement with the exp erimental data only at energies below the cross section maximum.