Structures and vibrations of phenol(NH3)(2-4) clusters

Vibronic spectra of PhOH(NH3)(n) clusters with n = 2-4 have been obtained b y resonant two-photon ionization, recorded at the mass channels of the frag ment ions (NH3)(n)H+. The PhOH(NH3)(2-4) spectra show long progressions of at least one low frequency vibration pointing to different S-0 and S-1 geom etries along this coordinate. In addition, the vibronic bands of the n=2 cl uster are split into two components. A tunneling motion is discussed, which may be responsible for these splittings. To get more information about the structure of PhOH(NH3)(2) in the electronic ground state, IR-UV double res onance spectroscopy has been applied. Possible geometries for the n = 2-4 c lusters are considered based on a comparison between the experimental data and theoretical results from ab initio calculations, performed at the Hartr ee-Fock and second-order Moller-Plesset perturbation theory level. (C) 2000 American Institute of Physics. [S0021-9606(00)00132-X].