The PFI-ZEKE photoelectron spectrum of m-fluorophenol and its aqueous complexes: Comparing intermolecular vibrations in rotational isomers

Pulsed field ionization–zero kinetic energy (PFI-ZEKE) photoelectron spectroscopy has been applied to study the cationic ground states of the rotational isomers of m-fluorophenol and its hydrogen-bonded clusters with H2O and D2O. The cis- and trans- monomer isomers are assigned by comparing the observed ionization potentials with values obtained from ab initio calculations (HF/6-31G*). Both monomers display very similar vibrational frequencies, indicating that the geometric structures of the two cations are similar. In contrast, the cis- and trans-aqueous clusters display distinctive intermolecular vibrational frequencies (e.g. the intermolecular stretching vibrations appear at 239 and 228 cm−1 in the cis- and trans-isomers respectively). The origin of the different intermolecular interactions in the isomeric clusters is discussed with reference to the ab initio calculations.