Session O8 - Molecular Clusters: From Dimers to the Condensed Phase III.
MIXED session, Thursday afternoon, March 20
Room 4202B, Conv. Center
The hydrogen-bonding topology of water clusters undergoes important changes from simple cyclic structures to more complicated three-dimensional networks beginning with the water hexamer. This paper will describe recent results from a combination of techniques which are providing ultraviolet and near-infrared spectra of size- and conformation-selected benzene-(water)_n clusters with n=846. One-color and two-color resonant two-photon ionization, ultraviolet hole-burning, and resonant ion-dip infrared (RIDIR) spectroscopies are used to assign and characterize these clusters. The OH stretch region of the infared provides a particularly rich probe of the hydrogen-bonding architecture of the clusters. Special emphasis will be placed on the benzene-(water)_7-9 clusters. In benzene-(water)_8, spectra due to two cubic structural isomers of water octamer, with nominal symmetry S_4 and D_2d, are identified and assigned on the basis of their comparison with ab initio calculations for the structures. In both cases the benzene molecule is attached to the surface of the cubic structure via a =BC H-bond with one of the dangling OH groups on the structure. The high symmetry and particular stability of these cubic structures provide a striking contrast to the tetra-coordinated structures which dominate the hydrogen bonding in liquid water and ice. Analogous results on larger clusters and on mixed benzene-(water)_n-(methanol)_m clusters will also be presented.