Vibronic and cation spectroscopy of selected rotamers of 4-chloro-3-fluorophenol

Abstract

We applied the two-colour resonant two-photon ionisation and mass-analysed threshold ionisation techniques to record the vibrationally resolved spectra of the selected rotamers and 35Cl and 37Cl isotopologues of 4-chloro-3-fluorophenol in the electronically excited S1 and cationic ground D0 states. The band origins of the S1 ← S0 electronic transition and the adiabatic ionisation energies of the cis and trans rotamers of 4-chloro-3-fluorophenol are determined to be 35,233 ± 2 and 35,405 ± 2 cm−1, and 69,334 ± 5 and 69,460 ± 5 cm−1, respectively. The electronic transition energies and general spectral features of the two isotopologues are nearly identical. Most of the observed active vibrations result from the in-plane ring deformation and substituent-sensitive motions. The experimental data show that the frequency difference in the observed active vibrations of the rotamers and isotopologues depends on the nature, vibrational pattern, location, and relative orientation of the substituents.