Femtosecond time-resolved spectroscopy of anionic systems: dynamics of mesoscopic systems and gas-phase organic reactions

摘要

This thesis work presents the femtosecond time-resolved spectroscopy of anionic systems ranging from gas-phase organic molecules to the finite-sized molecular clusters. The subject matter in this thesis is twofold: Mesoscopic solvation of anionic clusters and transition state dynamics of neutral organic molecules.Solvation dynamics in the finite sized clusters were investigated at the molecular level of details. The main objective of the cluster study was to follow the evolution of cluster properties as function of cluster size. Ultrafast processes exhibited in the cluster systems were investigated by utilizing the femtosecond time-resolved anion photoelectron spectroscopy. The bond rupture and solvent evaporation of homogeneous and heterogeneous clusters were studied, and the correlation between the dissociation rates and the cluster size is obtained. Gas-phase analogues of solvated systems were studied, and the key steps involved in the solvation dynamics are highlighted.Direct probing of the transition state dynamics in the ground state is studied with femtosecond time resolution. The transition state of the ring inversion reaction of cyclooctatetraene was directly accessed by the vertical detachment from the planar anion. The subsequent nuclear motion was then probed by ionization mass spectrometry. The oscillatory feature observed in the transients reflects trajectories of motion (resonance) along the reaction coordinate, and comparison with theory is reported. This work demonstrated the applicability of the charge reversal scheme to a complex organic system and suggests the possibility of studying ground-state thermal organic reactions with their transition states resolved in real time.