Abstract
We applied high-resolution resonant two photon ionization and mass analyzed threshold ionization spectroscopy to investigate the cationic properties of 4-fluoroindole, 5-fluoroindole and 6-fluoroindole. The obtained experimental data include the first electronic transition energy (E1) and ionization energy (IE) as well as the active vibrations in the electronically excited S1 and cationic ground D0 states. The E1 and IE of 4-fluoroindole are determined to be 35643 □ 2 cm-1 and 63523 □ 5 cm-1, whereas those of 5-fluoroindole are 34338 □ 2 cm-1 and 64326 □ 5 cm-1, 6-fluoroindole are 34980 □ 2 cm-1 and 63263 □ 5 cm-1, respectively. We also performed ab initio and density functional theory calculations to support our experimental findings. Analysis of our experimental results shows that most of the active modes of 4-, 5-, 6-fluoroindole in the S1 and D0 states are related to in-plane vibrations of the aromatic bicyclic ring.