Theoretical Characterization of the Structures and Vibrational Spectra of Benzene−(H₂O)n (n = 1−3) Clusters

The (H 2 O) n and benzene−(H 2 O) n ( n = 1−3) clusters have been characterized by means of the MP2 and density functional methods. The minimum-energy structures were optimized, and the harmonic frequencies were calculated for both the benzene−water clusters (BW n ) and the free water clusters (W n ). The W n clusters are π-hydrogen-bonded to the benzene ring, with the strength of this interaction being greatest for BW 2 . The geometries of the W n portions of the BW n clusters are found to be close to those of the free water clusters, with the perturbation due to the interaction with the benzene being greatest for BW 3 . For the OH stretching modes good agreement is found between the calculated and measured OH stretch IR spectra for both W n and BW n clusters. Both geometric and electronic ( i . e ., charge transfer/polarization interactions) effects are responsible for the significant changes in the OH stretch IR spectra brought about by the complexation of the water clusters with the benzene molecule.