A new class of free stable doubly negative systems: First investigations on the SimO2−n series

Studies on several isomers of the C2O2−n and Si2O2−n series of dianionic systems are performed at the Hartree–Fock, configuration interaction, Mo/ller–Plesset perturbation theory and outer-valence Green’s function levels of theory. All examined C2O2−n systems are predicted to be unstable with respect to electron autodetachment. However, the analogues silicon systems Si2O2−n turn out to be electronically more stable than the corresponding carbon species. For Si2O2−4 which marks the onset of electronic stability in the SimO2−n series the influence of the basis set and electron correlation on the geometrical parameters as well as on the electron detachment energy are studied in some detail. The possibility of decomposition via fragmentation or adiabatic electron loss is discussed. A simple criterion to determine whether a given structure may represent a promising candidate for a stable dianion of the SimO2−n type is suggested.