Mass analyzed threshold ionization of the 35Cl and 37Cl isotopomers of p-chloroaniline

One-color, two-color resonant two-photon ionization (R2PI), and mass analyzed threshold ionization (MATI) spectroscopic methods have been used to study the electronic transition and the threshold ionization of the Cl-35 and Cl-37 isotopomers of p-chloroaniline. The band origins of the S-1<--S-0 electronic transitions of both species are found to be 32 573 +/- 1 cm(-1). The ionization energies (IEs) of both isotopomers of p-chloroaniline are determined to be 62 409 +/- 7 cm(-1) by the two-color R2PI spectroscopy and 62 410 +/- 4 cm(-1) by the MATI spectroscopy. Analyses on the spectral features show that most of the active modes are related to the in-plane ring vibrations in the S-1 state and cationic ground state. Isotope effect on the ring deformation vibrations 1, 6a, and 12 gives rise to a frequency shift of 1-3 cm(-1) in the S-1 state and 3-9 cm(-1) in the ion state. The experimental results are well supported by the computed ones on the basis of ab initio and density functional theory calculations. (C) 2000 American Institute of Physics. [S0021-9606(00)01134-X].