A theoretical study of strong anharmonic coupling between OH stretching and bending modes in phenol–water cationic complex

The OH stretching vibrations of phenol (Ph), phenol cation ([Ph]+), phenol–water complex (Ph–H2O) and phenol–water cationic complex ([Ph–H2O]+) are investigated theoretically in terms of ab initio potential energy surfaces, vibrational wavefunctions, and infrared absorption intensities. It was found that the anharmonic coupling between the hydrogen-bonded OH stretching and bending vibrations in [Ph–H2O]+ is much stronger than those in Ph, [Ph]+ and Ph–H2O, resulting in vibrational wavefunction mixing and infrared intensity borrowing.