Hydrated hydronium: A cluster model of the solvated electron?

Ab initio (ROHF, CASSCF, CASPT2) and DFT/B3LYP calculations have been performed for the electronic ground state and the lowest excited singlet states of the water dimer and hydronium-water clusters. It has been found that a barrierless hydrogen-transfer reaction path exists in the first excited singlet state of the water dimer, leading to OH and H₃O radicals. The microsolvation of the hydronium radical has been investigated, considering up to two solvation shells of water molecules. Solvated H₃O is found to be a charge-separated complex, consisting of the hydronium cation and a localized electron cloud, which are connected by a water network. Results are reported on the stability of these clusters and their electronic and vibrational spectroscopic properties. The calculated electronic and vibrational spectra of the clusters exhibit striking similarities with the spectral signatures of the hydrated electron. It is argued that H₃O(H₂O)_n clusters could be the carriers of the characteristic spectroscopic properties of the hydrated electron.