Resonant Ion-Dip Infrared Spectroscopy of Ternary Benzene−(Water)n(Methanol)m Hydrogen-Bonded Clusters

Abstract

Resonant two-photon ionization, IR−UV hole-burning, and resonant ion-dip infrared (RIDIR) spectroscopies have been employed along with density functional theory (DFT) calculations to assign and characterize the hydrogen-bonded topologies and structures of eight benzene−(H2O)n(CH3OH)m, cluster isomers (hereafter shortened to BWnMm) with n + m ≤ 4. The O−H stretch infrared fundamentals are used to determine the H-bonding topology of the clusters. However, in several cases, the O−H stretch spectrum leaves an ambiguity regarding the position of the methanols within the structure. In these cases, the methyl CH stretch region serves as a secondary probe capable of distinguishing among the various possibilities. For n + m = 2, a single BWM isomer is observed with OH stretch fundamentals at 3508, 3606, and 3718 cm-1. A comparison of the methyl CH stretch transitions of BWM and BM2 reveals that the methanol in BWM accepts a H-bond from water and forms a π H-bond with benzene. The n + m = 3 results show the subtle ...