INFRARED SPECTROSCOPY OF LARGER BENZENE-(H$2O) n$ HYDROGEN-BONDED CLUSTERS: EVIDENCE OF CUBIC STRUCTURES

Author Institution: Department of Chemistry, Purdue University; Department of Chemistry, University of PittsburghOne color R2PI-TOFMS, ultraviolet hole-burning, and RIDIRS have been used lo assign and characterize (he hydrogen-bonding topology of size-selected benzene-$(H_{2}O)_{n}$ dusters formed in a supertonic molecular beam. Hole-burning spectroscopy confirms the presence of conformers in the increasingly congested R2PI spectra of these larger clusters. Two transitions in the benzene-$(H_{2}O)_{6}^{+}$ R2PI-TOFMS are assigned to the benzene-$(H_{2}O)_{8}$ cluster. Comparison of the experimental RIDIR spectra to density functional theory calculation results in the assignment of these conformer to cubic octamers of $S_{4}$ and $D_{2d}$ symmetry. The presence of benzene weakly distorts the cubic structures, breaking the degeneracy of several OH stretch vibrations and inducing intensity in otherwise forbidden infrared transitions. Four transitions in the benzene-$(H_{2}O)^{+}_{7}$ R2PI-TOFMS are tentatively assigned as two conformers each of the $(benzene)_{2}-(H_{2}O)_{8}$ benzene-$(H_{2}O)_{9}$ clusters. The RIDIRS of these species share common features with those of the cubic benzene-$(H_{2}O)_{8}$ octamers; thus, a structure for the benzene-water nonamer built by adding one water molecule to a cubic octamer is tested against calculations