A COMBINED EXPERIMENTAL AND THEORETICAL INVESTIGATION OF C2H2(2+) ELECTRONIC-STATE ENERGIES

Double-charge-transfer spectroscopy has been used to investigate low-lying electronic states of C2H22+. The projectile ion used was OH+ and, because of spin conservation in the double-electron-capture reaction which 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 ground 3SIGMA(g)- state, the 3PI(u) state and the 3PI(g). state, respectively. Incorporating the present data with previously determined singlet-state data, and with computed values, provides a comprehensive electronic-state distribution for C2H22+ up to 13 eV above the ground state. Vertical double-ionization energies calculated in the present investigation using a modified MSXalpha method are in accurate agreement with this distribution.