Charge separation and charge transfer to solvent in NaCl–water clusters

The electronic structure of NaCl–wn (w ≡ H2O and n = 1–6, 8) clusters was investigated by ab initio and time dependent density functional theory calculations. Upon photoexcitation, when n < 5 the electronic density migrates from one of the Cl valence p orbitals to the Na atom. When n ⩾ 5, the electronic density associated with one of these orbitals delocalizes over the nearby water molecules indicating the formation of CTTS states in the clusters. When n ⩾ 6, contact ion-pair (CIP) and solvent separated ion-pair (SSIP) structures are found. The onset of charge separation in the ground state of small NaCl–water clusters seems to coincide with the formation of CTTS states upon photoexcitation.