The O–H stretching vibrations in the hydrogen bonded (PHENOL)2+ radical cationic dimer. A gradient-corrected hybrid Hartree–Fock-density functional study

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–H⋯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 ν(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.