The origin of the S1<--S0 electronic transition and the adiabatic ionization energy of p-fluorophenol are determined to be 35117+/-2 and 68577+/-5 cm(-1), which are lower than those of phenol by 1232 and 48 cm(-1), respectively. Most of the active vibrations in the electronic excited S-1 and cationic ground D-0 states are related to the in-plane ring modes. The p-fluoro substitution not only causes red shifts in the transition energies but also leads to a decrease in the frequencies of the observed vibrations. The present experimental findings are well supported by our ab initio and density functional calculations. (C) 2004 Elsevier B.V. All rights reserved.