Characterization of the Hydrogen-Bonded Cluster Ions [Phenol−(H2O)n]+ (n = 1−4), (Phenol)2+, and (Phenol−Methanol)+ As Studied by Trapped Ion Infrared Multiphoton Dissociation Spectroscopy of Their OH Stretching Vibrations

Abstract

OH stretching vibrations of hydrogen-bonded cluster ions of phenol (PhOH), [PhOH−(H2O)n]+ (n = 1−4), (PhOH)2+, and (PhOH−methanol)+ have been observed with infrared photodissociation spectroscopy in combination with an ion-trapping technique. Cluster ions were efficiently generated by ionization of phenol followed by a jet expansion and were mass-selectively stored by the radio frequency ion trap method, which allows us to observe infrared multiphoton dissociation yield spectra of size-selected cluster ions. For [PhOH−(H2O)n]+, the OH stretching vibrations of the water moieties strongly suggested that the n ≥ 3 cluster ions exhibit the proton-transferred form, [PhO−H3O+(H2O)n-1], while the n = 1 and 2 ions are of the nontransferred form, [PhOH+−(H2O)n]. As for (PhOH)2+, the infrared spectra indicate that the dimer ion is characterized as the open form, in which the phenol ion acts as a proton donor and the neutral phenol as an acceptor through their single hydrogen bond. The similar open form is also foun...