The Rydberg Nature And Assignments Of Excited States Of The Water Molecule

We report ab initio theoretical calculation on 32 excited states of H₂ O found to lie below 11.7 eV. Of the eight states observed experimentally, the average discrepancy between theoretical and experimental excitation energies is 0.1 eV. We find that the excited states can each be characterized as arising from an excitation to a Rydberg orbital. Our results indicate that the Ẽ and F̃ states are both 3d-like excited states rather than one 3d state and one 4s state as previously assumed and similarly for the two Rydberg series joining onto Ẽ and F̃. The nsa₁ Rydberg series is found to have a quantum defect of 1.38. joining onto the Ã(¹B₁ state. We have assigned the 9.81 eV transition observed by electron impact as the 1b₁ - 3pb₁ excitation to a ³A₁ state.