Photon-emission studies of slow C4+-Ne collisions

We present absolute term- and level-selective cross sections for specific single- and double-electron capture processes in slow (16 keV) C4+-Ne collisions. The results are deduced through a combined analysis of earlier translational energy-gain data and the present photon-emission cross sections in the region 40 endash 240 nm. We find that double-electron capture is dominated by processes in which two electrons appear to change orbitals in a single interaction of two diabatic quasimolecular potential curves emdash a type of process which rarely has been isolated before. Furthermore, we observe a strong preference for population of 2s2p over 2p2 configurations in these one-step two-electron capture reactions. This is a remarkable configuration selectivity, since reaction channels leading to 2s2p and 2p2 configurations cross with the incident channel at almost the same internuclear distances. copyright 1997 The American Physical Society