The potential energy function of the 1 1Σ + u excited state of CO 2, which lies around 11 eV above the electronic ground state, has been investigated by ab initio multiconfiguration self-consistent field calculations. It has been found that this state exhibits two minima on one-dimensional cuts of the potential energy function along the bending coordinate. One minimum at colinear geometry has a Rydberg character, whereas the other one located at a bending angle of about 140° has a valence character. Both minima are separated by a small barrier. This seems to be responsible for complicated splittings observed in the absorption spectrum of the first dipole-allowed electronic transition of CO 2.