CHARGE INVERSION OF GROUND-STATE AND METASTABLE-STATE C-2(-ENERGY() CATIONS FORMED FROM ELECTROIONISED C2H2 AND C2N2, AND A REEVALUATION OFTHE CARBON DIMERS IONIZATION)

Charge-inversion, translational-energy spectrometry has been used to p robe the electronic-state compositions of C-2(+) ion beams formed from electroionised acetylene and cyanogen, and to determine state-specifi c ionisation energies for C-2. It was found that C-2(+) ions were form ed predominantly in the (4) Sigma(g)(-) ground state when electrons of about 23 eV energy were used to ionise acetylene. Below this threshol d, and down to about 19 eV electron energy, the C-2(+) ions formed fro m C2H2 were found to be in the metastable (2) Pi(u) state, while above 23 eV the beams were of mixed-state composition. In contrast, ionisat ion of cyanogen by electrons with energies from about 18 to 100 eV app arently produced beams containing only C-2(+)((2) Pi(u)) ions. From th e energy-loss positions of observed spectral peaks, the energies for i onisation of C-2(($) over tilde X(1) Sigma(g)(+)) into the (4) Sigma(g )(-) and (2) Pi(u) states were deduced to be 11.4(1) +/- 0.30 and 12.3 (3) +/- 0.30 eV, respectively.