Fine-structure-dependent product branching in the ionization of Ar by Ne*(3s 3P2, 3P)

Using laser-state-selected metastable neon combined with mass spectrometric product detection in a crossed supersonic beam experiment, we have found a marked dependence of the fraction of associative ionization in Ne*+Ar Penning ionization on the initial fine-structure state of Ne*. Ne*(3P0) produces more NeAr+ than 3P2 relative to the total ionization cross section by amounts ranging from 33% more at E=1.5 kcal/mol to 72% at E=4.5.