Zero point corrections to vertical excitation energies

Equations relating the vertical excitation or ionization energy to the average energy of the observed spectrum are derived. For the V–N transition of ethylene, this gives 7.8 eV for the vertical excitation energy. For the vertical ionization of ethylene, the average energy yields 10.73 eV while correction to the observed 0–0 energy suggests that 10.81 eV is a more accurate value.