Energies of the lowest singlet and triplet states of molecular dications determined using O + and C + ion double-charge-transfer spectroscopy

Abstract

The potential for using O + and C + ions as projectiles in double-charge-transfer (DCT) spectroscopy has been investigated. Target-gas molecules of CO 2, OCS and CS 2 are shown to be double ionized into triplet states in reactions with ground-state O + and C + ions whereas the metastable ions in these beams populate singlet dication states. The superpositions of spectral peaks arising from these processes have allowed precise determinations to be made of the energy separation between lowest singlet and triplet states which are consistent with previous experimental and theoretical values. CH 4 target gas was also studied, the vertical double ionization energy to the 3T 1 state are being found to be 38.3 ± 0.4 eV and the separation between this state and the lowest singlet state 1E being 0.3 ± 0.2 eV. Additional peaks observed in the DCT spectra of C +( 2P) ions have been tentatively attributed to spin-disallowed processes or to reactions involving radiative loss.