Quantitative analysis of surface pH at water/air interface by phase-sensitive sum-frequency vibrational spectroscopy

KuoYang Chiang^1*, Laetitia Dalstein¹, YuChieh Wen¹

¹Institute of Physics, Academia Sinica, Taipei, Taiwan

* Presenter:KuoYang Chiang, email:Livius.Chiang@gmail.com

Water/air interface is one of the most significant platforms for many atmospheric and chemical processes in nature, and the reaction kinetics therein is unavoidably dictated by its surface pH. In the past two decades, many researches indicated that hydronium ions exhibit manifest surface propensity, resulting in a surface pH value different from the that in bulk solution. In this presentation, I shall report our recent development of phase-sensitive sum-frequency spectroscopy (PS-SFS) technique and its application to quantitative analysis of hydronium adsorption to the water/air surface. The PS-SFS technique can now provide vibrational spectra of the Stern layer and the diffuse layer near a water interface separately, so that structural and charge information of the water surface can be derived on the microscopic level. The results turn out quantitative Gibbs adsorption energy for the hydronium to the water surface for the first time, offering a basis for comparison with nowadays theoretical studies.

Keywords: air/water interface, phase-sensitive sum-frequency spectroscopy, hydronium