Metastable 3Σ−g ground state of F++2 and the bonding in molecular dications

Large multireference configuration interaction (MR-CI) calculations on the F++2 ion predict a 3Σ−g ground state, metastable with respect to tunneling into the F++F+ nuclear continuum. The potential energy curve displays a 0.40 eV barrier at Rb=1.607 Å, between the local potential minimum (Re=1.289 Å) and the 3Pg(F+)+3Pg(F+) asymptote at 7.69 eV lower energy. The potential barrier traps four quasibound vibrational levels, with a tunneling lifetime of 16 ms for v=0. A Dunham analysis at the well minimum gives ωe=919.4 cm−1, ωexe=16.31 cm−1, Be=1.073 cm−1, and αe=0.0316 cm−1. In a departure from an earlier viewpoint, the origin of the barrier in this and other dications is interpreted as a sum of the e2/R Coulomb repulsion and the ordinary chemical bonding of the constituent ions. This model also explains the purely repulsive character found for the valence-excited 1Δg and 1Σ+g states.