Resonant ion-dip infrared spectroscopy of benzene-(water) 9 : Expanding the cube The techniques of resonant two-photon ionization ͑R2PI͒, UV-UV ͑ultraviolet͒ hole-burning, and resonant ion-dip infrared ͑RIDIR͒ spectroscopies have been employed along with density functional theory ͑DFT͒ calculations to assign and characterize the hydrogen-bonding topologies of two isomers each of the benzene-͑water) 8 and (benzene͒ 2 ͑water) 8 gas-phase clusters. The BW 8 isomers ͑Bϭbenzene, Wϭwater͒ have R2PI spectra which are nearly identical to one another, but shifted by about 5 cm Ϫ1 from one another. This difference is sufficient to enable interference-free RIDIR spectra to be recorded. As with smaller BW n clusters, the BW 8 clusters fragment following photoionization by loss of either one or two water molecules. The OH stretch IR spectra of the two BW 8 isomers bear a close resemblance to one another, but differ most noticeably in the double-donor OH stretch transitions near 3550 cm Ϫ1 . Comparison to DFT calculated minimum energy structures, vibrational frequencies, and infrared intensities leads to an assignment of the H-bonding topology of the BW 8 isomers as nominally cubic water octamers of S 4 and D 2d symmetry surface attached to benzene through a H-bond. A series of arguments based on the R2PI and hole-burning spectra leads to an assignment of additional features in the R2PI spectra to two isomers of B 2 W 8 . The OH stretch RIDIR spectra of these isomers show them to be the corresponding S 4 and D 2d analogs of B 2 W 8 in which the benzene molecules each form a H-bond with a different dangling OH group on the W 8 sub-cluster.

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