Rotational analysis and tunnel splittings of the intermolecular vibrations of the phenol-water complex by high resolution UV spectroscopy

Highly resolved (Delta nu<100 MHz) UV-REMPI (ultraviolet-resonantly enhanced multiphoton ionization) spectra of different vibronic bands in the phenol-water complex are presented. The torsional splitting caused by the hindered rotation of the water moiety in the hydrogen-bonded system is investigated. An autocorrelation procedure reveals torsional subbands, a correlation automated rotational fitting (CARF) of the spectra yields the rotational constants: The analyzed vibrations are classified by the rotational constants of the corresponding vibronic band and the symmetry of the torsional state, The transition to the stretching vibration at 156 cm(-1) excess energy is shown to consist of two different torsional transitions similar to the electronic origin. The torsional splitting in the origin band is 0.8491(2) cm(-1) and that of the stretching vibration is 0.8915(3) cm(-1), demonstrating a very small coupling between the stretching and the torsional motion. We assign the 121 cm(-1) band as the negative parity component of the transition to the wagging vibration beta(2) while the band at 125 cm(-1) is tentatively assigned as the positive parity component of the same band. The resulting large torsional splitting of -4.596(3) cm(-1) points to a strong coupling to the torsional motion. The band at 95 cm(-1) has only one torsional parity component within its rotational envelope. The observed large change of its rotational constants does not fit to the pattern of the other vibrations and the band is tentatively assigned as an overtone of the torsional vibration tau with positive parity. (C) 1998 American Institute of Physics.