Electron affinities of CO2, OCS, and CS2

The structure of the CO2−, OCS−, and CS2− anions as well as the adiabatic electron affinities of the corresponding CO2, OCS, and CS2 neutral parents are computed using the infinite-order coupled-cluster method with all singles and doubles and non-iterative inclusion of triple excitations (CCSD(T)) and Hartree-Fock-Density-Functional-Theory (HFDFT) levels of theory. The potential energy curves of the CO2 – CO2− and CS2 – CS2− pairs are calculated as a function of the bending angle. All three anions are found to have bent equilibrium configurations. The adiabatic electron affinities of CO2 and OCS are calculated to be negative, whereas the CS2− anion is stable in the linear and relaxed geometries. The existence of CS2− at linear geometries can be related to experimental observations of an electric field-induced detachment of an extra electron from the anion in fields of only a few kilovolts per centimeter.