Hydration of potassium iodide dimer studied by photoelectron spectroscopy and ab initio calculations.

We measured the photoelectron spectra of (KI)(HO) (n = 0-3) and conducted ab initio calculations on (KI)(HO) anions and their corresponding neutrals up to n = 6. Two types of spectral features are observed in the experimental spectra of (KI)(HO) and (KI)(HO), indicating that two types of isomers coexist, in which the high EBE feature corresponds to the hydrated chain-like (KI) while the low EBE feature corresponds to the hydrated pyramidal (KI). In (KI)(HO), the (KI) unit prefers a pyramidal configuration, and one of the K-I distances is elongated significantly, thus a K atom is firstly separated out from the (KI) unit. As for the neutrals, the bare (KI) has a rhombus structure, and the structures of (KI)(HO) are evolved from the rhombus (KI) unit by the addition of HO. When the number of water molecules reaches 4, the K-I distances have significant increment and one of the I atoms prefers to leave the (KI) unit. The comparison of (KI)(HO) and (NaI)(HO) indicates that it is slightly more difficult to pry apart (KI) than (NaI) via hydration, which is in agreement with the lower solubility of KI compared to that of NaI.