Surface Propensities of Atmospherically Relevant Ions in Salt Solutions Revealed by Phase-Sensitive Sum Frequency Vibrational Spectroscopy
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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<sup>–</sup>, NO<sub>3</sub><sup>–</sup>, NH<sub>4</sub><sup>+</sup>, Cl<sup>–</sup>, K<sup>+</sup>, Na<sup>+</sup>, and SO<sub>4</sub><sup>2-</sup>. Most of our results agree with predictions of MD simulations, but NO<sub>3</sub><sup>–</sup>and NH<sub>4</sub><sup>+</sup> do not