STATE-SELECTIVE ONE-ELECTRON CAPTURE FROM HE, NE AND AR BY 4 KEV STATE-PREPARED C2+ IONS

A new instrument to carry out double-translational energy spectroscopy (DTES) recently developed in this laboratory has been described in de tail. This permits studies of state-selective electron capture by slow state-prepared multiply charged ions using translational energy spect roscopy (TES). The effectiveness and future potential of this approach has been illustrated by studies of one-electron capture in helium, ne on and argon by 4 keV beams of pure ground-state C2+(1s(2)2s(2))S-1 an d pure metastable C2+(1s(2)2s2p)P-3 ions. In each case the main produc t channels have been identified by TES and analysed quantitatively wit hout the ambiguities associated with previous measurements which used primary ion beams containing a mixture of ground and metastable specie s. A simple beam attenuation technique has also been used in conjuncti on with our state-prepared beams to provide estimates of the ratios si gma(P-3)/sigma(S-1) of the total one-electron capture cross sections w hich, in each case, show that sigma(P-3) is considerably larger than s igma(S-1). These ratios have in turn been used to show that the metast able content of C2+ ions from the present ECR ion source and sources u sed in other laboratories can be substantial.