The lowest potential energy curves, for the electronic states of the molecule ZnO in the representation 2s+1 Λ (+/−) have been performed via Complete Active Space Self Consistent Field (CASSCF) using the Multireference Configuration Interaction (MRCI) method with Davidson correction (+Q). An excitation and de-excitation model has been proposed, in analogy to the emission of ZnO nanoparticles. In addition, the minimum energy level with respect to the ground state, Te, the internuclear distance at equilibrium, Re, the rotational constant, Be, the vibrational frequency, ωe, and the static and transition dipole moment, μ, have been investigated for some electronic states. Thirteen new electronic states have been studied here for the first time.