The competition of Penning ionization and ion pair formation in fast collisions of metastable rare gas atoms with O2 and Cl2 molecules

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Abstract
Integral ionization cross sections have been measured for collisions of the metastable rate gas atoms He(2 3S), Ne(2p53s), and Ar(3p54s) with the molecular targets O2 and Cl2 in the energy range 30 to 1000 eV by collecting the slow mass‐analyzed target ions X+,X+2 and X−,X−2, where X stands for O and Cl. The cross sections for ion pair formation yielding X− and X−2 ions are found to be strongly influenced by the presence of continuum and energy transfer channels. The energy dependence of the cross sections for Penning ionization leading to the formation of X+ and X+2 ions is, on the other hand, strongly altered by the presence of low‐lying ionic states of the type Rg+–X−2, where Rg stands for a rare gas atom. The energy dependence of the efficiency for secondary electron emission by the metastable rare gas atom He*(2 3S), Ne*(2p53s), Ar*(3p54s), and Kr*(4p55s) is presented for kinetic energies between 80 and 1000 eV.