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

作者：Mercedes Rubio, Luis Serrano‐Andrés, Manuela Merchán · 发表于：The Journal of Chemical Physics · 年份：2008 · DOI：10.1063/1.2837827 · 被引用次数：79 · 研究领域：Advanced Chemical Physics Studies、Spectroscopy and Quantum Chemical Studies、Photochemistry and Electron Transfer Studies

The excited states of the water molecule have been analyzed by using the extended quantum-chemical multistate CASPT2 method, namely, MS-CASPT2, in conjunction with large one-electron basis sets of atomic natural orbital type. The study includes 13 singlet and triplet excited states, both valence and 3s-, 3p-, and 3d-members of the Rydberg series converging to the lowest ionization potential and the 3s- and 3p-Rydberg members converging to the second low-lying state of the cation, 1 (2)A(1). The research has been focused on the analysis of the valence or Rydberg character of the low-lying states. The computation of the 1 (1)B(1) state of water at different geometries indicates that it has a predominant 3s-Rydberg character at the equilibrium geometry of the molecule but it becomes progressively a valence state described mainly by the one-electron 1b(1)-->4a(1) promotion, as expected from a textbook of general chemistry, upon elongation of the O-H bonds. The described valence-Rydberg mixing is established to be originated by a molecular orbital (MO) Rydbergization process, as suggested earlier by R. S. Mulliken [Acc. Chem. Res. 9, 7 (1976)]. The same phenomenon occurs also for the 1 (1)A(2) state whereas a more complex behavior has been determined for the 2 (1)A(1) state, where both MO Rydbergization and configurational mixing take place. Similar conclusions have been obtained for the triplet states of the molecule.