Charge transfer and atomic rearrangement in collisions of

A new apparatus designed to perform photoelectron product-ion coincidence (PEPICO) measurements is described. The collision system Ar+(2P12,32) + H2 is studied as a first test case. Relative cross sections for ArH+ and H2+ formation by the two fine structure states of the ion are measured at three average center-of-mass collision energies, 0.05, 0.075 and 0.125 eV. The results are interpreted in the context of data available in the literature and confirm the importance of a vibronic resonance for the Ar+(2P12)+H2 system at low collision energies.