Potential energy surfaces of excited states of H2−

Thirteen electronic states of H2− in various symmetries have been calculated using the MRCI/aug-cc-pV5Z approximation. The lowest 2Σu+ and 2Σg+ states have been shown to cross with the X 1Σg+ state of H2 at the nuclear separation of 1.58 and 2.70 Å and the energies of 3.16 and 4.66 eV, respectively. The surfaces of higher excited states exhibit complex shapes defined by avoided crossings between the states of the same symmetry. Some of the excited H2− and H2 surfaces cross, and this crossing can be relevant to the electron attachment processes in laser-irradiated H2.