Vibrational spectroscopy at the ice-air interface: a molecular-level picture of the quasi-liquid layer

Ice interfaces play vital roles in several chemical reactions, phase transitions, and crystal growth. To investigate these surfaces, vibrational sum-frequency generation (vSFG) spectroscopy has been used extensively owing to its intrinsic surface specificity. Although the first experimental vSFG spectra at the ice-air interface were recorded two decades ago, a comprehensive theoretical understanding of the OH stretching region within the spectra and the role of the quasi-liquid layer in the melting process of ice remains elusive. In this work, we employ the MB-pol(2023) water potential energy surface combined with path-integral-based quantum dynamics methods to characterize the vSFG spectrum of the ice-air interface. We will present our findings on the melting behavior of ice and the vSFG spectra at the ice-air interface, and discuss the origins of the spectral peaks with respect to hydrogen bonding topologies and molecular orientations.