Microsolvation of Sodium Thiocyanate in Water: Gas Phase Anion Photoelectron Spectroscopy and Theoretical Calculations.

We studied NaSCN(H2O)n- clusters in the gas phase using size-selected anion photoelectron spectroscopy. Vertical detachment energies (VDEs) of NaSCN(H2O)n- (n = 0-6) clusters were obtained in the experiment. Structures of NaSCN(H2O)n- (n = 0-6) clusters and their corresponding neutral counterparts were investigated by theoretical calculations. Our studies show that the Na-NCS type of structures rather than the Na-SCN type of structures are dominant in the gas phase for both anionic and neutral NaSCN(H2O)n clusters. For NaSCN(H2O)n- anions, the contact ion pair (CIP) and solvent-separated ion pair (SSIP) type of structures coexist at n = 2 and 3, the SSIP type of structures become dominant at n ≥ 4. For neutral NaSCN(H2O)n, the CIP type of structures are dominant from n = 1 to 6 and the SSIP type of structures start to appear at n = 6. The gas phase structures in this work support the existence of ion clustering in concentrated NaSCN aqueous solutions.