Calculation of the Excitation Energies. Calculations of excited-state wave functions were carried out by state-averaged CASSCF, averaging over the ground state and the minimum necessary number of excited states of the symmetry specified by QUESTDB. For example, in a C 2v molecule (e.g., water) if the symmetry of the excited state under consideration is specified to be 1 A 2 with no lower 1 A 2 excitations present, then the state averaging was done evenly over the 1 A 1 ground state and the 1 A 2 excited state. For higher 1 A 2 excitations, however, the state averaging included an additional 1 A 2 state for each 1 A 2 excitation lower in energy (again with weights for state averaging being the same for all states averaged).