Ab Initio Study of Sum-Frequency Vibrational Spectroscopy of Interfacial Water under Fermi Resonance

Water plays a vital role in sustaining life and mediating processes across diverse scientific disciplines. Its interfacial behavior is particularly critical in fields such as energy, atmospheric science, materials science, and biology. Sum-frequency vibrational spectroscopy (SFVS), a surface-specific nonlinear optical technique, enables detailed investigations of molecular structure and dynamics at various interfaces. In this study, we employ ab initio molecular dynamics and quantum chemistry calculations to examine the influence of Fermi resonance between bending vibrational overtones and stretching modes on SFVS of the interfacial water. Our results show that although the Fermi resonance modifies the SFVS of the stretching mode, the SFVS features of interfacial water are primarily governed by the electric dipole and quadrupole contributions.