SEARCH Articles Figures Tables Electron vibrations Electron-excitation states Electronic excited Electronic excited states Electronic perturbation Electronic perturbed Electronical excitation Electrons excitation Electrons, excited Excited States Ordering Ordered state Perturbation order Perturbed state Second excitation Second excited Second excited state Second-order theory Second-order vibrational perturbation theory Vibration excitation Vibration excited Vibration theory Vibrational electronics Vibrational excited state Vibrationally excited