Mass analyzed threshold ionization spectroscopy of 3-aminopyridine cation and vicinal substitution effect

The mass analyzed threshold ionization spectra of 3-aminopyridine (3AP) were recorded via the 0(0), 10b(1), 10b(1)I(1), 6a(1), 1(1), and 12(1) levels in the S, state. The adiabatic ionization energy of this molecule was determined to be 65,229 +/- 5 cm(-1) (8.0869 +/- 0.0006 eV). These new experimental data suggest that the molecular geometry and vibrational features of the 3AP cation resemble those of the neutral species in the S, state. Comparing the present results with those of 2-aminopyridine and aniline provides insights into the vicinal substitution effects on the electronic transition, threshold ionization, and molecular vibration of aromatic molecules. We have also performed ab initio and density functional calculations, which provide satisfactory interpretation for our experimental findings. (C) 2002 Elsevier Science B.V. All rights reserved.