The global minimum on B3LYP, mPW1PW91 and PBE1PBE/6-31++G(d,p) potential energy surfaces (PESs) of the (phenol)(2)(+) cationic radical dimer corresponds to O-H+...O hydrogen-bonded structure, with an additional, although much weaker C-(HO)-O-... hydrogen bond, as revealed by AIM analysis. Excellent agreement with experimental data is obtained for the anharmonic vibrational frequency shift of the dangling O-H oscillator on the basis of one-dimensional DFT O-H stretching potentials. However, theoretical calculations suggest that the nu(O-H+...O) mode due to the hydrogen-bonded O-H oscillator should appear at significantly lower frequencies than it was first estimated on the basis of experimental dissociation spectroscopy combined with an ion trap technique data. (C) 2003 Elsevier Science B.V. All rights reserved.