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

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.