Mass analyzed threshold ionization of deuterium substituted isotopomers ofaniline and p-fluoroaniline: Isotope effect and site-specific electronic transition

Two-color resonant two-photon mass analyzed threshold ionization (MATI) spe ctroscopy was used to record the threshold ion spectra of deuterium-substit uted isotopomers of aniline and p-fluoroaniline. The respective adiabatic i onization energies of C6H5NH2, C6H5NHD, C6H5ND2, C6D5NH2, C6D5NHD, C6D5ND2, p-FC6H4NH2, p-FC6H4NHD, and p-FC6H4ND2 were determined to be 62 271, 62 25 3, 62 233, 62 258, 62 237, 62 214, 62 543, 62 520, and 62 507 cm(-1) with a n uncertainty of about 5 cm(-1). Analyses on the shifts in the electronic t ransition and ionization energies prove that the S-1<--S-0 transition mainl y 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. (C) 2 001 American Institute of Physics.