Structure and vibrations of phenol⋅CH3OH (CD3OD) in the electronic ground and excited state, revealed by spectral hole burning and dispersed fluorescence spectroscopy

The intermolecular vibrations of phenol(CH3OH)1 and its deuterated isotopomer d-phenol(CD3OD)1 were examined by comparing the vibrational frequencies of the electronic ground and excited state with the results of ab initio normal mode calculations at the Hartree–Fock level, using the 4-31G* and 6-31G** basis sets. Full energy minimization showed a translinear structure similar to phenol(H2O)1 or to the water dimer. Dispersed fluorescence spectra have been recorded via excitation of the electronic cluster origin and several intermolecular vibrational transitions. The Franck–Condon intensity pattern allowed an assignment of the ground state vibrational frequencies to the excited state frequencies, which were examined by resonance enhanced multiphoton ionization and hole burning spectroscopy. The existence of another conformer that possibly absorbs in the region of interest was ruled out by hole burning spectroscopy of the phenol(CH3OH)1 cluster. A full assignment of all intermolecular vibrations of this hydrogen bonded cluster in the S0 state could be given for the first time on the basis of ab initio calculations and a combination of different spectroscopical methods.