SCF ab-initio computations are performed for the ground states of CO 2 and CO2-. The CO2 and CO 2- potential surfaces have been obtained over a large region of space; in particular, the intersection of these two surfaces. Our results predict that the stability of CO2- depends strongly on whether it is formed near the equilibrium bond angle (135°), the most stable situation, or at significantly different angles. The calculations show that the 6α1 molecular orbital of CO2- is diffuse in character and that the computed equilibrium geometry (bond angle, 135.3°, bond length, 2.35 bohr) and electron affinity (-0.36 eV) are consistent with experiment. Copyright © 1975 American Institute of Physics.