Surface Propensities of Atmospherically Relevant Ions in Salt Solutions Revealed by Phase-Sensitive Sum Frequency Vibrational Spectroscopy

We use phase-sensitive sum-frequency vibrational spectroscopy (PS-SFVS) to study the air/water interfaces of a set of salt solutions. The spectra reveals the presence of an electric double layer formed by cations and anions at the interfaces, and allow us to find the relative surface propensities of different ions in the following decreasing ranking order: I(-), NO(3)(-), NH(4)(+), Cl(-), K(+), Na(+), and SO(4)(2-). Most of our results agree with predictions of MD simulations, but NO(3)(-) and NH(4)(+) do not.