Ionization energy of p-fluoroaniline and vibrational levels of p-fluoroaniline cation determined by mass-analyzed threshold ionization spectroscopy

Mass-analyzed threshold ionization (MATI) and two-color resonant two-photon ionization (2C-R2PI) methods were used for detailed studies of the adiabatic ionization energy of p-fluoroaniline (PFA) and the vibrations of this molecule in the cationic ground state. The threshold ion spectra were recorded for PFA via the 0 degrees vibrationless and the 6a(1), 1(1), 12(1), 6a(1)l(1), and 6a(1)12(1) vibrational levels of the SI state. The adiabatic ionization energy of PFA is found to be 62 543 +/- 4 cm(-1) by the MATI spectroscopy and 62 550 +/-. 7 cm-l by the 2C-R2PI spectroscopy. Results show that the active modes are mostly related to in-plane ring vibrations of the ion. All of these experimental data are presented for the first time. Ab initio and density functional theory calculations were also performed for predicting the ionization energy and vibrational frequencies. Comparative studies show that the measured and calculated results are in very good agreement.