Ionization, energetics, and geometry of the phenol-S complexes (S = H2O, CH3OH, and CH3OCH3)

The present study combines both experiment and molecular modeling to describe the photoionization behavior of the gas-phase hydrogen-bonded complexes of phenol with water, methanol, and dimethyl ether, in particular the occurrence of fragmentation following ionization. Using the two-color two-photon resonant ionization laser technique, the threshold for dissociative ionization of these species has been measured. For the first time, precise binding energies have been deduced for the neutral species: D-0(phenol-H2O) = 243 +/- 5 meV and D-0(phenol-CH3OH) = 265 +/- 8 meV. Using a semiempirical potential model, the minimum energy structures of both neutral and ionic species have been determined. This theoretical study has emphasized the role of the dispersive interactions in the geometry of these neutral complexes, in particular the interactions between the alkyl group of the solvent molecule (CH3 in the case of methanol or dimethyl ether) and the pi-cloud of the aromatic molecule. In addition, the comparison between the neutral and ionic geometry of these complexes has allowed us to account qualitatively for the changes in the ionization properties within the complex series, namely in their zero kinetic-energy photoelectron spectra.