Rotamers of 2,5-Difluorophenol Studied Using Mass-Analyzed Threshold Ionization Spectroscopy

We applied resonant two-photon ionization (R2PI) and mass-analyzed threshold ionization (MATI) techniques to record the vibronic and cationic spectra of 2,5-difluorophenol. The distinct bands at 36448 and 36743 cm(-1) were confirmed as the origins of the S-1 <- S-0 So electronic transition of the cis and trans rotamers, respectively. The corresponding adiabatic ionization energies were found to be 71164 and 71476 cm(-1) for these two rotameric species. The observed spectral features mainly result from the in-plane ring deformation and substituent-sensitive bending vibrations. Spectral analysis suggests that the molecular geometry and vibrational coordinates of the cation in the Do state resemble those of the neutral species in the S-1 state for both cis and trans rotamers.