Absorption spectra of H₂O and D₂O molecules in the vacuum-ultraviolet region

Excited states of the water molecule: Analysis of the valence and Rydberg character

“…In contrast, the CCSDR͑3͒ vertical excitation energies for the 1b 1 → 3d Rydberg states are 0.2-0.3 eV overestimated with respect to our MS-CASPT2 results and the experimental data. 13 A better agreement is, however,…”

“…15,16 The observed bands were interpreted as Rydberg series on the basis of the quantum defect analysis and using available ab initio calculations as a guide for the assignments. [11][12][13][16][17][18][19] A comprehensive ab initio study on the excited states of water performed in 1974 by Goddard and Hunt 17 characterized all the computed states below 11.7 eV as having Rydberg nature, a result supported at the configuration interaction ͑CI͒ level. 18,19 As shall be discussed below, the electronic spectrum of water in the gas phase is currently interpreted as composed either of different Rydberg series or implying excited states with a significant Rydberg character at the ground-state equilibrium geometry ͑see, for instance, Ref.…”

“…Assignments based on the defect quantum number analysis also situate the 3d-members of the Rydberg series converging to the lowest ionization potential at these energies. 11,13 In particular, Ishiguro et al 13 recorded three bands with maximum at 10.99, 11.05, and 11.13 eV which were ascribed to the optically allowed 1b 1 → 3d Rydberg states. According to the present calculations, these three bands correspond, respectively, to the 1 B 1 ͑1b 1 → 3d͒, 1 1 B 2 ͑1b 1 → 3d xy ͒, and both 1 A 1 ͑1b 1 → 3d xz ͒ and 1 B 1 ͑1b 1 → 3d͒ states.…”

“…The 1b 1 → 3d Rydberg transitions have been experimentally located in the 10.8-11.2 eV energy range, [11][12][13][14]16 which is definitely confirmed by the present MS-CASPT2 results ͑see Table III͒. Thus, the computed ͗r 2 ͘ values as well as the directionality of the electronic charge distribution characterize the singlet excited states calculated between 10.8 and 11.2 eV as the five components of the 1b 1 → 3d Rydberg promotions.…”

“…Experimental evidence for the 2 1 B 2 state comes from a study performed by Dutuit et al 23 These authors proposed the 2 1 B 2 state as responsible for the continuous absorption recorded in the energy range 10.0-12.6 eV, centered at around 11.5 eV. Taking into account the great complexity of the electronic spectrum of water at energies above 11.0 eV, 12,13 together with the low intensity values predicted for the 3a 1 → 3p x and 3a 1 → 3p z Rydberg transitions, their experimental locations have not been determined, as far as we know. According to the MS-CASPT2 results, both states are located close to the lowest ionization potential of the molecule ͑ϳ12.6 eV͒, 50 where the absorption spectrum is dominated by the 1b 1 → nd transitions.…”