Nonlinear Scaling of Water-Ion Interactions and Dynamics in Alkaline Solutions

Water-ion interactions govern many solvent properties critical to solution-phase chemistry and the behavior of liquid water. The water-ion interactions in alkaline conditions were probed using two-dimensional infrared spectroscopy (2D IR), small-angle x-ray scattering (SAXS), and nuclear magnetic resonance spectroscopy (NMR). Energy transfer between the donor molecule KSeCN, used as a 2D IR probe, and the acceptor molecule NaOD was used to track the average separation distance of ions in a D2O solution, while SAXS measurements showed effects in the bulk D2O solvent. We observe consistent nonlinear scaling in the SeCN- and OD- average separation distance as a function of NaOD concentration while bulk solution D2O-to-D2O average separation distance remained highly linear. Ultrafast measurements of solution dynamics via 2D IR and polarization-selective pump-probe spectroscopy show consistent scaling in correlation times as a function of concentration. These results suggests that the SeCN- and OD- anions participate in a water-ion network that significantly reduces the degrees of freedom for the distribution of ions in solution below the standard stochastic for ion distribution.. Authors: Felsted, Robert G.; Mergelsberg, Sebastian T.; Graham, Trenton R. (ORCID:0000000189078004); Bazak, Jonathan D.; Pearce, Carolyn I.. DOE Contract: AC05-76RL01830. Subjects: 2D IR Spectroscopy; Aqueous Structure; Small-Angle X-Ray Scattering; Water-Ion Network; Solution Order