Electrolytes Change the Interfacial Water Structure but Not the Vibrational Dynamics.

Malte Deiseroth,Mischa Bonn,Ellen H. G. Backus

doi:10.1021/acs.jpcb.9b08131

Abstract

Heterogeneous ozone chemistry occurring on aerosols is driven by interfacial chemistry and thus affected by the surface state of aerosol particles. Therefore, the effect of electrolytes on the structure of interfacial water has been under intensive investigation. However, consequences for energy dissipation rates and mechanisms at the interface are largely unknown. Using time-resolved sum frequency generation spectroscopy, we reveal that the relaxation pathway is the same for neat water-air as for aqueous solutions of Na2SO4 and Na2CO3. We further show that similar lifetimes are extracted from all investigated systems and that these lifetimes show an excitation frequency dependent relaxation time from 0.2 ps up to 1 ps. Hence, despite static SFG on the same systems revealing that the interfacial aqueous structure changes upon adding electrolytes, the vibrational dynamics are indistinguishable for both pure water and different electrolyte solutions.

Highlights

Physical and chemical processes occurring at aqueous interfaces have been shown to play a prominent role in a variety of fields ranging from the chemistry of atmospheric aerosols and heterogeneous catalysis to biophysics and biochemistry
To study the vibrational energy flow, we present the first study on the vibrational dynamics of the water stretch vibration under the influence of ions
To investigate the impact of ions on the structure and the vibrational dynamics of the water−air interface, we first turn toward the structure

Summary

Introduction

Physical and chemical processes occurring at aqueous interfaces have been shown to play a prominent role in a variety of fields ranging from the chemistry of atmospheric aerosols and heterogeneous catalysis to biophysics and biochemistry. Roughly 30% of the CO2 released by human activity in the past few decades has been uptaken by the ocean and a large part of it resides in the form of CO32− within the ocean itself.[6]

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