OH stretching vibrations of the phenol(H2O)1+ cation

In this Letter, we report on the application of infrared/photo induced Rydberg ionisation (IR/PIRI) spectroscopy to the hydrogen-bonded phenol(H2O)1+ cluster yielding the frequency of the symmetric OH stretching vibration of the bare cluster ion. By comparing IR/PIRI and IR-photodissociation spectra the symmetric OH stretching mode of the water moiety turns out to be a localised uncoupled vibration. Furthermore, CASSCF calculations for the phenolic OH stretching vibration of phenol(H2O)1 in the S0, S1, and D0 states are performed by using a very large active space including σ- and π-orbitals. These calculations yield OH stretching frequencies which are in good agreement with the experimentally observed vibrational frequencies of the S0 and S1 states. The OH stretching vibration of the D0 state is predicted to be lower than 2800 cm−1.