IR double-resonance spectroscopy applied to the 4-aminophenol(H2O)1 cluster

The IR double-resonance techniques IR/R2PI (infrared/resonant 2-photon ionization), IR/PIRI (infrared-photo-induced Rydberg ionization) and IR-photodissociation spectroscopy are valuable tools to investigate structure, vibrations, and dynamical processes of neutral and ionic hydrogen-bonded clusters containing aromatic molecules. In this paper we report on the application of the IR double-resonance techniques to determine the NH and OH stretching vibrations of 4-aminophenol and 4-aminophenol (H2O)(1), both in the neutral (S-0) and ionic (D-0) ground state. All vibrational frequencies obtained for 4-aminophenol and the cluster are compared with the values obtained from ab initio and DFT calculations. In the S-0 state, a trans-linear arrangement of 4-aminophenol (H2O)(t) is obtained containing an O-H . .O hydrogen bond. In the D-0 state an overlay of two spectra can be observed resulting from the trans-linear structure and a second structure which contains a N-H . .O hydrogen bond. The observation of these two structures within the ion is an interesting example of a rearrangement reaction in the ionic state.