Microscopic solvation of NaBO2 in water: anion photoelectron spectroscopy and ab initio calculations

We investigated the microscopic solvation of NaBO2 in water by conducting photoelectron spectroscopy and ab initio studies on NaBO2-(H2O)(n) (n = 0-4) clusters. The vertical detachment energy (VDE) of NaBO2- is estimated to be 1.00 +/- 0.08 eV. The photoelectron spectra of NaBO2-(H2O)(1) and NaBO2-(H2O)(2) are similar to that of bare NaBO2-, except that their VDEs shift to higher electron binding energies (EBE). For the spectra of NaBO2-(H2O)(3) and NaBO2-(H2O)(4), a low EBE feature appears dramatically in addition to the features observed in the spectra of NaBO2-(H2O)(0-2). Our study shows that the water molecules mainly interact with the BO2- unit in NaBO2-(H2O)(1) and NaBO2-(H2O)(2) clusters to form Na-BO2-(H2O)(n) type structures, while in NaBO2-(H2O)(3) and NaBO2-(H2O)(4) clusters, the water molecules can interact strongly with the Na atom, therefore, the Na-BO2-(H2O)(n) and Na(H2O)(n)center dot center dot center dot BO2- types of structures coexist. That can be seen as an initial step of the transition from a contact ion pair (CIP) structure to a solvent-separated ion pair (SSIP) structure for the dissolution of NaBO2.