Infrared Spectrum of a Molecular Ice Cube: The <i>S</i> ₄ and <i>D</i> ₂ _<i>d</i> Water Octamers in Benzene-(Water) ₈

Abstract

Resonant two-photon ionization, ultraviolet hole-burning, and resonant ion-dip infrared (RIDIR) spectroscopy were used to assign and characterize the hydrogen-bonding topology of two conformers of the benzene-(water) 8 cluster. In both clusters, the eight water molecules form a hydrogen-bonded cube to which benzene is surface-attached. Comparison of the RIDIR spectra with density functional theory calculations is used to assign the two (water) 8 structures in benzene-(water) 8 as cubic octamers of D 2 d and S 4 symmetry, which differ in the configuration of the hydrogen bonds within the cube. OH stretch vibrational fundamentals near 3550 wave numbers provide unique spectral signatures for these “molecular ice cubes.”