High-resolution photoelectron imaging, photodetachment spectroscopy, and the dipole-bound state of the 2,3-difluorophenoxide anion

Fluoroaromatic compounds play an important role in material chemistry, where the fluorine substituents can strongly influence molecular stability and polarity. The 2,3-difluorophenol is a valuable precursor for fluoro-compounds, but its spectroscopic and electronic properties or those of the 2,3-difluorophenoxide anion (DFP-) and the DFP radical have not been well characterized. Here, we report a combined high-resolution photoelectron imaging, photodetachment spectroscopy (PDS), and resonant photoelectron spectroscopy (rPES) investigation of the cryogenically cooled DFP- anion. The electron affinity of the DFP radical is measured accurately to be 2.7000(6) eV and its first excited state is observed at an excitation energy of 1.05 eV. PDS reveals a dipole-bound state at 225 cm-1 below the detachment threshold of DFP-, along with 20 vibrational Feshbach resonances. Relaxations from the zero-point level of the dipole-bound state to a triplet excited state and the vibrational levels of the ground state of DFP- are observed using resonant two-photon PES. The rPES at the Feshbach resonances exhibits strong mode-specific vibrational autodetachment and new non-Franck-Condon vibrational features. Vibrational frequencies for 12 fundamental vibrational modes of the DFP radical are obtained, including four out-of-plane bending modes.