STATE-SELECTIVE ONE-ELECTRON CAPTURE BY 4 KEV GROUND-STATE, AND METASTABLE C2-2, N-2 AND O-2( IONS IN COLLISIONS WITH H)

The technique of double translational energy spectroscopy (DTES) has b een used in a recently developed apparatus to study (for the first tim e) one-electron capture. by state-prepared C2+ ions in collisions with H-2, N-2 and 02 molecules, These processes:are relevant to astrophysi cal situations, planetary atmospheres and to the modelling and diagnos tics of edge plasmas in current fusion devices. The main collision cha nnels resulting from state-selective electron capture by pure beams of 4 keV S-1 ground state and P-3 metastable C2+ ions have been separate ly identified and their relative importance determined without any of the ambiguities inherent in TES studies normally carried out Sith ion beams of unknown metastable content. At the energy considered, only no n-dissociative electron capture is observed with collision channels in volving capture into the C+ (2s2p(2))S-2 D-2, P-4 and C+ (2s(2)2p)P-2 states together with the formation of H-2(+), N-2(+) and O-2(+) in gro und and electronically excited states. Our measurements indicate that some of these molecular ions have significant degrees of vibrational e xcitation in accord with the Franck-Condon factors for the relevant tr ansitions. Striking differences between the collision channels for S-1 ground and P-3 metastable ions are observed.