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

摘要

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 C_6H_5NH_2, C_6H_5NHD,C_6H_5ND_2, C_6D_5NH_2,C_6D_5NHD, C_6D_5ND_2, p-FC_6H_4NH_2. p-FC_6H_4NHD, and p-FC_6H_4ND_2 were determined to be 62271, 62253, 62233, 62258, 62237, 62214, 62543, 62520, and 62507 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_o transition mainly occurs around the aromatic ring whereas the transition from the neutral, 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 initlo and density functional calculations.