Electronic structure of the water dimer cation

P.A. Pieniazek, J. VandeVondele, P. Jungwirth, A.I. Krylov, and S.E. Bradforth
J. Phys. Chem. A 112, 6159 – 6170 (2008)

The spectroscopic signatures of proton transfer in the water dimer cation were investigated. The six lowest electronic state were characterized along the reaction coordinate using the equation-of-motion coupled-cluster method with single and double substitutions for ionized systems. The nature of the dimer states was explained in terms of the monomer states using a qualitative molecular orbital framework. We found that the proton transfer induces significant changes in the electronic spectrum, thus suggesting to employ time-resolved femtosecond spectroscopy to monitor the dynamics following ionization. The electronic spectra at vertical and proton-transferred configurations include both local excitations (features similar to those of the monomers) and charge-transfer bands. Ab initio calculations were used to test the performance of a self-interaction correction for density functional theory (DFT). It is found that the corrected DFT/BLYP method is capable of reproducing the correct ordering of the (H₂O)₂⁺ isomers, and thus may be employed in calculations of larger systems.

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