ANIONIC AND NEUTRAL STATES OF LI3O

The ground state of the cation, three lowest electronic states of the neutral, and two anionic states of Li3O were studied using different ab initio techniques. Stationary points on the potential energy surfaces were determined both at complete active space (CAS) self-consistent field (SCF) and at second-order Moller-Plesset (MP2) levels of theory. Excited states were approached using the single-excitation configuration interaction (CIS) method. Electron detachment energies for the anionic and neutral states were calculated at the quadratic configuration interaction (QCI) level with single, double, and approximate triple excitations (SD(T)) included, The calculations indicate that Li3O- possesses two bound electronic states. The ground (1)A(1)' state has an equilibrium D-3h structure and a vertical electron detachment energy (VDE) of 0.66 eV. The (3)E' bound state pseudorotates through (3)A(1) and B-3(2) stationary points. The barrier for pseudorotation was found to be less than 0.002 eV at the QCISD(T) level. Two VDE peaks for the (3)E' anion were predicted to be at 0.45 and 1.15 eV for transitions to the ground and the first excited state of the neutral, respectively. The ground state of the cation and the first three electronic states of the neutral Li3O were also considered, and the vertical ionization potential for the ground neutral state was found to be 3.60 eV. Li3O and Li3O- are thermodynamically stable with respect to the unimolecular decompositions Li3O (neutral or anion) --> Li2O + Li (neutral or anion). Hence, the species should be amenable to experimental studies.