Slow-electron velocity-map imaging study of aniline via resonance-enhanced two-photon ionization method

Slow electron velocity-map imaging (SEVI) of aniline has been investigated via two-color resonant-enhanced two-photo (1 + 1') ionization (2C-R2PI) method. A number of vibrational frequencies in the first excited state of neutral (S-1) and B-2(1) ground electronic state of cation (D-0) have been accurately determined. In addition, photoelectron angular distributions (PADs) in the two-step transitions are presented and reveal a near threshold shape resonance in the ionization of aniline. The SEVI spectra taken via various S-1 intermediate states provide the detailed vibrational structures of Do state and directly deduce the accurate adiabatic ionization potential (IP) of 62,271 +/- 6 cm(-1). Ab initio calculations excellently reproduce the experimental IP value (Theo. 62,242 cm(-1)). For most vibrational modes, good agreement between theoretical and experimental frequencies in the S-0 and D-0 states of aniline is obtained to aid us to clearly assign vibrational modes. Especially, the vibrational frequencies calculated at the CASSCF level are much better consistent with experimental data than that obtained using the TDDFT and CIS methods. (C) 2016 Elsevier B.V. All rights reserved.