Resonant ion-dip infrared spectroscopy of benzene-(water)(n)-(methanol)(m)clusters with n+m=4,5

Resonant two-photon ionization and resonant ion-dip infrared (RIDIR) spectr a of benzene-(water)(n)-(methanol)(m) clusters thereafter shortened to BWnM m) have been recorded for a total of seven clusters with n + m = 4 and 5. T he infrared spectra in the OH and CH stretch regions show absorptions chara cteristic of H-bonded WnMm clusters which are bound to benzene by a pi H-bo nd involving a dangling OH on the WnMm sub-unit. Density functional theory (DFT) calculations identify a number of conformational isomers in the n + m = 4 series which meet the general criteria imposed by the experimental spe ctra. The structures, binding energies, harmonic vibrational frequencies, a nd infrared intensities for these isomers have been calculated for comparis on with experiment. Based on the calculations, tentative assignments of sev eral of the observed species are given. The calculations uncover the fact t hat complexation of benzene to the cyclic water tetramer imposes much the s ame perturbations on the cycle as substitution of methanol for water. In pa rticular, the single-donor OH stretch spectra of WnMm and BWn+1Mm-1 are cal culated to be virtually identical to one another. The comparison of experim ent and theory for this series of cyclic structures is used to assess the s trengths and limitations of the calculations at the DFT Becke3LYP/6-31 + G * level of theory. (C) 1998 Published by Elsevier Science B.V. All rights r eserved.