Infrared and electronic spectra of size-selected phenol cluster ions, (phenol)n+ for n = 2-4, were observed by using dissociation spectroscopy combined with an ion trap technique. Vibrational spectra of the OH stretching region indicate that the dimer ion has an asymmetric form such that the ionic moiety acts as a proton donor and that the trimer and tetramer ions have noncyclic forms with respect to intermolecular hydrogen bonds. In the electronic spectra of (phenol)n+ in the range of 400-1600 nm was found no charge resonance transition except for a transition due to the local excitation of the phenol ion moiety. The result indicates that charge delocalization interaction between phenyl rings is not significant in these cluster ions. It was concluded that all the phenyl moieties in the trimer ion are bound by a linear chain of the OH⋯O hydrogen bonds, while a symmetric form with cyclic hydrogen bonds has been established for the neutral trimer. The OH stretching vibration of the hetero dimer ion of (phenol-benzene)+ was also observed, in which the phenol ion is expected to be bound onto the benzene ring through a π-type hydrogen-bond. An extremely large red-shift and a substantial broadening of the OH band of the phenol ion moiety were found, and the results were discussed in respect to the characteristic feature of hydrogen-bonded OH vibrations of ionic clusters.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry