First-principles investigations on and oxocarbons

Comprehensive first-principles calculations on the geometrical and electronic properties of C 5 O 5 - / 0 and C 6 O 6 - / 0 oxocarbons have been performed in this work. Both C 5 O 5 - monoanion and C5O5 neutral are found to possess perfect planar pentagonal structures at their ground states D5h C 5 O 5 - ( 2 A 2 ″ ) (1) and D5h C5O5 ( 1 A 2 ′ ) (2), while C 6 O 6 - and C6O6 appear to favor the slightly distorted quasi-planar C2v C 6 O 6 - (2A1) (3) and C2v C6O6 (1A1) (4), respectively. Adaptive natural density partitioning (AdNDP) analyses clearly reveal the σ- and π-bonding patterns of the monocyclic C n O n 2 - / - / 0 oxocarbons (n = 5 and 6). The adiabatic detachment energies (ADEs) and low-lying vertical detachment energies (VDEs) of the monoanions have been calculated at the coupled cluster level with triple excitations (CCSD(T)), with ADE = 3.723 and VDE = 3.776 eV for C 5 O 5 - and ADE = 3.629 eV and VDE = 3.679 eV for C 6 O 6 - CCSD(T)//MP2. The first excited states of the neutrals are predicted to have the approximate term values of T1 = 1.08 eV (3A2) for C5O5 and T1 = 1.22 eV (3B1) for C6O6. The predictions made in this work may help facilitate experimental characterizations of C 5 O 5 - and C 6 O 6 - monoanions.