A combined experimental and theoretical investigation of C 2H 2+2 electronic-state energies

Abstract

Double-charge-transfer spectroscopy has been used to investigate low-lying electronic states of C 2H 2+ 2. The projectile ion used was OH + and, because of spin conservation in the double-electron-capture reaction with is central to this type of spectroscopy, it was expected that triplet states of the dication would be populated. Three peaks in the spectrum were observed corresponding to vertical double-ionization energies of 32.7 ± 0.3, 37.9 ± 0.4 and 39.6 ± 0.5 eV. By comparing these with calculated data, the energies are identified with the groun 3Σ − g state, the 3Π u state and the 3Π g state, respectively. Incorporating the present data with previously determined singlet-state data, and with computed values, provides a comprehensive electronic-state distribution for C 2H 2+ 2 up to 13 eV above the ground state. Vertical double-ionization energies calculated in the present investigation using a modified MSXα method are accurate agreement with this distribution.