Infrared Spectrum of a Molecular Ice Cube: The S ₄ and D _{2 d} 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.”

Accurate Energies and Structures for Large Water Clusters Using the X3LYP Hybrid Density Functional

“…40 Among these threedimensional structures there is some disagreement on the detailed structure of the decamer but not for the octamer, which has a cubic structure. 41,42 As expected, water octamer isomers (D 2d and S 4 ) have similar energies in both X3LYP and MP2 calculations 42,43 (Table 3). Water decamers appear in both X3LYP and MP2 calculations to prefer a pentagonal prism structure over a less symmetric "butterfly" form derived from the cubic octamer.…”

Novel water clusters in the crystalline state: structures of a symmetrical, cyclic hexamer and an ‘opened-cube’ octamer

“…4 Each of these isomers has oxygen atoms at the corners of a cube with hydrogen bonds along each edge; they differ only in the details of the hydrogen bonding. Evidence for the presence of both of these isomers has been found in gas-phase C 6 H 6 (H 2 O) 8 clusters 7 and in molecular beams. 8 An octameric cluster with a cubic arrangement of oxygen atoms has also been reported in a solid-state hydrate, but in this case the hydrogen atoms were not located.…”

“…3 The most stable conformations for water clusters of various degrees of aggregation have been predicted on the basis of ab initio electronic structure calculations. 4 A number of clusters, including hexamers and octamers, have been characterized spectroscopically in the gas phase, [5][6][7] in molecular beams 8 and in liquid helium droplets. 9 Clusters with n = 6, 8 and 10 have been found in crystalline hydrates.…”

Characterization of the (D2O)2 Hydrogen-Bond-Acceptor Antisymmetric Stretch by IR Cavity Ringdown Laser Absorption Spectroscopy

“…New infrared and far-IR spectroscopic methods have revealed a wealth of detail regarding structures, hydrogen-bond tunneling dynamics, and intermolecular vibrational motions in water clusters as large as the octamer. [1][2][3] Ab initio calculations have provided much insight into the intermolecular potential energy surfaces (IPS) governing their properties, 4 and new dynamical techniques 5,6 have made it possible to interpret the high-resolution spectra of these clusters directly in terms of the many-body dynamics occurring on the IPS.…”