Asymmetric Hydrogen-Bonding Structure at a Water/Ice Interface

The interface between liquid water and the basal plane of crystal ice Ih at the melting point temperature is investigated via molecular dynamics (MD) simulations to examine the molecular structure and the interface-specific vibrational sum frequency generation (VSFG) spectrum. It is believed that the OH bonds of the water molecules near the water/ice interface have no preferential orientation. With enough sampling, the present MD simulation results show that water molecules slightly direct their protons toward the water phase in average to form hydrogen bonding (H-bonding) networks toward a highly dense liquid phase. Moreover, a clear VSFG response is found at the water/ice interface despite its weak orientational structure, indicating the imaginary susceptibility opposite to the average orientational structure. The molecular mechanism of the VSFG response is discussed regarding the asymmetric H-bonding structure at the water/ice interface, which is further compared with the structures and vibrational spectra at the water/air and ice/air interfaces.