Energy curves of CO−2

Abstract

Ab initio energy curves of the 2A1 and 2B1 states of CO−2 are reported as a function of the bending angle. The 2A1 curve is found to be bound relative to the neutral curve at angles greater than 130° from the linear geometry. Both the 2A1 and 2B1 states are found to be valence in character for the geometries considered and the excitation energy for 2A1 → 2B1 is calculated to be 3.2 eV in the neighborhood of the CO−2 equilibrium geometry while the experimental value for the maximum in the lowest absorption curve is almost 3.5 eV. From the bending energy curve it is deduced that gaseous CO−2 in its ground vibrational level can have a relatively long life since the ion energy in the neighborhood of the ion equilibrium geometry is about 1 eV below the neutral molecule energy for that geometry.