Double ionization energies to form the C 2H 2+6 ion in triplet ground and electronically excited states

Abstract

Double ionization energies to various triplet electronic states of C 2H 2+ 6 have been measured by double charge transfer spectroscopy using OH + as the projectile ion. Four peaks were observed in the spectrum, corresponding to double ionization energies (in eV) of 32.1 ± 0.4, 33.5 ± 0.3, 35.2 ± 0.5 and 36.4 ± 0.5. The first of these is associated with the ground triplet state. The double ionization energy to this state was calculated using the GAUSSIAN 86 ab initio program package at the Hartree—Fock level with second order Møller—Plesset perturbation theory. Seven basis sets were tried; the predicted energy with each is within ± 0.2eV of 32.1eV. A previous theoretical investigation of C 2H 2+ 6, using the Green's function method, predicted the energy spacings between the triplet states. When energies lying so close together as to be unresolvable experimentally are grouped together, the spacings between the double ionization energies measured in the present investigation and those calculated are in good agreement.