Sum-frequency vibrational specstrocopy of the bending mode of water at interfaces

We apply the mixed quantum/classical method and neural network-based molecular dynamics simulations to investigate sum-frequency vibrational spectroscopy (SFVS) of the bending vibration of the interfacial water. By analyzing the contributions of the electric dipole, electric quadrupole, magnetic dipole, and non-resonant mechanisms in SFVS, we demonstrate that electric quadrupole interactions play a dominant role in both the imaginary part of the SSP SFVS and the real and imaginary parts of the PPP SFVS. Conversely, the non-resonant contribution primarily influences the real part of the SSP SFVS signal. These findings significantly enhance our understanding of SFVS data interpretation by elucidating the underlying mechanisms governing the bending vibration at liquid interfaces. The results provide critical insights into resolving existing contradictions observed in SFVS studies, particularly concerning bending vibrational characteristics.