Vibronic and cation spectroscopy of 2,4-difluoroaniline.

We applied the two-color resonant two-photon ionization and mass-analyzed threshold ionization techniques to record the vibronic and cation spectra of 2,4-difluoroaniline. The cation spectra were recorded by ionizing via the 0(0), X(1), 6b(1), and 1(1) levels of the electronically excited S(1) state. Most of the observed active modes of this molecule in the S(1) and cationic ground D(0) states are related to the in-plane ring deformation vibrations. The band origin of the S(1)←S(0) electronic excitation was found to appear at 33294 ± 2 cm(-1), whereas the adiabatic ionization energy was determined to be 63935 ± 5 cm(-1). Comparing the data of 2,4-difluoroaniline with those of aniline, 2-fluoroaniline, and 4-fluoroaniline, one can learn the effects of fluorine substitution on the electronic transition and molecular vibration.