Taken together, the VSFG results show that a unique sub-population of interfacial water emerges or breaks inversion symmetry when both Na and CO 3 2are present near the cathode. This suggests the formation of interfacial ion-complexes with a unique solvation environment, since the spectral peak emerges most strongly in the presence of both ions. The formation of ion-paired complexes is plausible under the concentrations we consider with typical ion-ion separations on the order of the Na-CO 3 Bjerrum length, 26 λ B = 14 Å, in water. We consider the results of MD simulations to gain microscopic insight into (1) the thermody- namics of forming Na-CO 3 ion-complexes and how this may change near the interface, (2) the structure of these complexes and their orientation relative to the interface, and (3) the vibrational spectrum and orientation of waters that give rise to the vibrational peak seen in the VSFG spectra.