Two-color resonant two-photon mass analyzed threshold ionization (MATI) spectroscopy was used to record the threshold ion spectra of deuterium-substituted isotopomers of aniline and p-fluoroaniline. The respective adiabatic ionization energies of C6H5NH2, C6H5NHD, C6H5ND2, C6D5NH2, C6D5NHD, C6D5ND2, p-FC6H4NH2, p-FC6H4NHD, and p-FC6H4ND2 were determined to be 62 271, 62 253, 62 233, 62 258, 62 237, 62 214, 62 543, 62 520, and 62 507 cm(-1) with an uncertainty of about 5 cm(-1). Analyses on the shifts in the electronic transition and ionization energies prove that the S-1<--S-0 transition mainly occurs around the aromatic ring whereas the transition from the neutral S-1 to the cationic state corresponds to the removal of one of the lone-pair electrons of nitrogen. The present results provide the first experimental evidence for the site-specific electronic transition in aniline as well as the isotope effects on the vibrations of the aniline cation. These findings are well supported by ab initio and density functional calculations.