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

Abstract

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 <i>relative</i> surface propensities of different ions in the following decreasing ranking order: I^–, NO₃^–, NH₄⁺, Cl^–, K⁺, Na⁺, and SO₄^2-. Most of our results agree with predictions of MD simulations, but NO₃^–and NH₄⁺ do not