HIGH RESOLUTION UV SPECTROSCOPY OF PHENOL AND THE HYDROGEN BONDED PHENOL/WATER CLUSTER

Author Institution: University of Nijmegen, 6525 ED Nijmegen. The Netherlands; Heinrich-Heine Universität Düsseldorf, 40225 Düsseldorf, GermanyPhenol and the hydrogen bonded Phenol$(H_{2}O)_{1}$ cluster have been studied by high resolution fluorescence excitation spectroscopy. The $S_{1} \leftarrow S_{0} 0^{0}_{0}$ vibronic transitions of the monomer and cluster were observed. All lines in the monomer spectrum are split by $56 \pm 4$ MHz due to the internal rotation of the OH group around the C-O bond. The rotational constants for the monomer were found to be $A^{\prime\prime}=5650.452 MHz. B^{\prime\prime}=2619.190 MHz, C^{\prime\prime}=1789.843 MHz and A^{\prime}=5313.6 MHz, B^{\prime}=2620.5 MHz; C^{\prime}=1756.7 MHz$, simulated with a rotational temperature of 5K. The region of the 0,0 transition of Phenol$(H_{2}O)_{1}$ shows two distinct bands which are $0.85 cm^{-1}$ apart. The analysis of both bands showed, that they arise from the vibrational/torsional motion, which interchanges the two equivalent H-atoms in the $H_{2}O$ moiety of the cluster. This assignment was further confirmed by spin statistical considerations, which led to the inevitable conclusion, that the cluster has a symmetry plane bisecting the water moiety. A barrier of $140 cm^{-1}$ could be estimated for the electronic ground state and $120 cm^{-1}$ for the electronically excited state. The analysis of the rotational constants of the cluster yielded a O-O distance of the hydrogen bond of 2.865 A in the electronic ground state and 2.824 A in the electronically excited state