Resolving the Spectral Signatures of Strong Hydrogen Bonding in Fluoride Hydration

The fluoride ion forms some of the strongest hydrogen bonds in aqueous solution, making its hydration shell an ideal system to probe the interplay between ion--water interactions, hydrogen-bond dynamics, and nuclear quantum effects (NQEs). In this study, we integrate MB-nrg data-driven many-body potential energy functions with advanced quantum dynamics simulations to uncover how many-body interactions and NQEs shape the structure and vibrational response of hydrated fluoride. Our analysis reveals that short-range three-body interactions between the ion and surrounding water molecules are critical for capturing the infrared spectral features of the first hydration shell, particularly in the OH-stretch and libration regions. We identify distinct reorientation dynamics of OH bonds that give rise to the bifurcation of the libration band. While NQEs induce a redshift in OH-stretching frequencies, they have minimal influence on orientational and translational dynamics. These results underscore the importance of rigorous many-body treatments to achieve predictive accuracy in modeling ion hydration and interpreting vibrational spectra.