title: Investigation of electronically excited indole relaxation dynamics via photoionization and fragmentation pump-probe spectroscopy.
abstract: The studies herein investigate the involvement of the low-lying (1)La and (1)Lb states with (1)ππ(*) character and the (1)πσ(*) state in the deactivation process of indole following photoexcitation at 201 nm. Three gas-phase, pump-probe spectroscopic techniques are employed: (1) Time-resolved photoelectron spectroscopy (TR-PES), (2) hydrogen atom (H-atom) time-resolved kinetic energy release (TR-KER), and (3) time-resolved ion yield (TR-IY). Each technique provides complementary information specific to the photophysical processes in the indole molecule. In conjunction, a thorough examination of the electronically excited states in the relaxation process, with particular focus on the involvement of the (1)πσ(*) state, is afforded. Through an extensive analysis of the TR-PES data presented here, it is deduced that the initial excitation of the (1)Bb state decays to the (1)La state on a timescale beyond the resolution of the current experimental setup. Relaxation proceeds on the (1)La state with an ultrafast decay constant (<100 femtoseconds (fs)) to the lower-lying (1)Lb state, which is found to possess a relatively long lifetime of 23 ± 5 picoseconds (ps) before regressing to the ground state. These studies also manifest an additional component with a relaxation time of 405 ± 76 fs, which is correlated with activity along the (1)πσ(*) state. TR-KER and TR-IY experiments, both specifically probing (1)πσ(*) dynamics, exhibit similar decay constants, further validating these observations.
authors.affiliation: Department of Physics and Astronomy, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Godfrey
authors.affiliation: Department of Physics and Astronomy, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: Hui
authors.initials: H
authors.lastname: Yu
authors.affiliation: Department of Physics and Astronomy, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: Susanne
authors.initials: S
authors.lastname: Ullrich
mesh_terms: D004583:Electrons; D007211:Indoles / Q000737:chemistry* / Q000528:radiation effects; D007477:Ions / Q000737:chemistry; D007700:Kinetics; D007834:Lasers; D055668:Photochemical Processes; D013057:Spectrum Analysis / Q000379:methods*
chemical_list: D007211:Indoles; D007477:Ions; C030374:indole