Studies of 4-chloro-2-fluoroanisole by two-color resonant two-photon mass-analyzed threshold ionization spectroscopy

We applied the two-color resonant two-photon mass analyzed threshold ionization technique to record the cation spectra of 4-chloro-2-fluoroanisole by ionizing via five intermediate vibronic levels. The excitation and adiabatic ionization energies were determined to be 35 227, and 67 218 \wn, respectively. Spectral analysis and theoretical calculation suggest that the geometry of the aromatic ring of the neutral species in the S$_{1}$ state is non-planar, but that of the cation in the D$_{0}$ state is planar