Vibrational Sum Frequency Generation Spectroscopy VSFG, a surface-specific technique, is widely utilized for studying molecular orientation, dynamics, and chemical reactions on surfaces. Previous studies have reported the detection of free OH stretch of interfacial water at the aqueous dielectric interface using VSFG. However, it has only recently been observed at the Auelectrolyte interface under applied potential. This feature indicates the presence of interfacial water with one non-hydrogen-bonded OH group directed toward the Au electrode, supporting the hydrophobic nature of the Au surface as observed in previous work by Tong et al. The broad peak around 3650 cm -1 can be assigned to weakly hydrogen-bonded or singly hydrogen-bonded water. The absence of the peak around 3200 cm -1 , which corresponds to strongly hydrogen bonded water, in the spectra presented in Figure suggests that the water structure at the gold electrode surface is relatively disordered as suggested by Nihonyanagi et al. When more negative applied potential, a new peak around 3,400 cm -1 becomes evident for both electrolytes. However, the peak is much more prominent for Na 2 CO 3 than Cs 2 CO 3 . This peak might be associated with either liquid-like water or a hydrogen-bonded water network with a coordination lower than the tetrahedral water found around 3200 cm -1 . In our previous study, this peak was attributed to Na + and CO 3 2-ion pair or ion association. To determine the origin of this feature, we investigated the influence of different electrolyte compositions on the water structure at the interface. NaCl and Na 2 SO 4 were chosen to compare with Na 2 CO 3 . As shown in Figure , the peak is not very pronounced in Ar-purged NaCl and is almost absent in Ar-purged Na 2 SO 4 solutions, but is more evident in Ar-purged Na 2 CO 3 electrolyte. This observation confirms that the feature around 3,400 cm -1 is enhanced when carbonate is present at the interface. Given these observations, we attribute the feature to the effect of a carbonate species present in the electrochemical double layer on the water structure. We notice that this peak appears at relatively negative potentials. It might be counter intuitive that anions can influence the water orientation at a negatively charged electrode surface. However, despite their negative charge, anions can be attracted to a Au surface even when a negative potential is applied because of their ion pairing interactions with cations, or because of specific molecular driving forces. In a previous study by Zou et al., it was discovered that the effect of the anion on the Raman spectra of water is significant, even at very negative potentials. They attributed this to the formation of ion pairs at the electrochemical interface. The combination of Figures and suggest that the presence of both Na + and CO 3 2-is needed to enhance the intensity of the 3400 cm -1 feature, providing indirect evidence for ion pairing interactions.