The structure of phenol in the S1-state determined by high resolution UV-spectroscopy

The structure of phenol in the electronically excited S-1-state has been examined by rotationally resolved UV-spectroscopy of different isotopomers of phenol. The geometry has been fit to the inertial parameters of 12 isotopomers, using different pseudo-Kraitchman fitting strategies. The resulting r(0), r(s), r(m)((1)), and r(m)((2)) structures, which differ in the amount of consideration of vibrational effects, will be compared among one another as well as to the results of published ab initio studies: The geometry of the -COH substructure has been determined separately for both electronic states by applying Kraitchman's equations. Independent of the fitting strategy we found a shortening of the CO bond, an increase of the OH bond length and an expansion of the aromatic ring upon electronic excitation. The internal rotation of the hydroxy group causes line splittings that could be observed in the case of the OH species, but remained unresolved for all OD isotopomers. The S-1-state lifetimes of the different isotopomers are shown to depend mainly on the presence of the OH function and depend less on the exchange of CH by CD. Thus, the OH stretching mode is most likely the dominant accepting mode, responsible for the rapid internal conversion in phenol. (C) 2002 Elsevier Science B.V. All rights reserved.