Structures and vibrations of neutral and cationic 3-and 4-aminophenol

A combined experimental and theoretical study on the structures and vibrations of 3- and 4-aminophenol in their neutral and ionic ground states is presented. The vibrations of the two possible isomers of 3-aminophenol and the one isomer of 4-aminophenol are investigated by mass analyzed threshold ionization (MATI) spectroscopy in the ionic ground state and by infrared resonant 2-photon ionization (IR/R2PI) spectroscopy in the neutral ground state. The experimentally observed vibrational frequencies of all isomers are in excellent agreement with the calculated values obtained by density functional theory (DFT) and at the complete active space self-consistent field (CASSCF) level of theory. The calculations support the assignment of different isomers. Furthermore, the experimentally observed ionization potentials are well predicted by CASMP2//CASSCF calculations. (C) 2004 Elsevier B.V. All rights reserved.