Investigating gas-phase molecular structures and structural dynamics with Coulomb explosion imaging

  • Lingfeng Ge

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Scientists have developed a variety of ultrafast pump-probe experimental techniques to investigate gas-phase molecular structural dynamics over the past few decades. Amongst those techniques is Coulomb explosion imaging, which can provide direct information on nuclear positions. Coulomb explosion imaging takes advantage of ionisation-dissociation of gas-phase molecules and velocity map imaging of fragment ions. In our research group, an NIR laser was used to perform strong field ionisation on small molecules for Coulomb explosion imaging. A new laser beam system was built for this purpose, and a peak laser intensity of 1300 TW/cm² was achieved in the interaction area with molecules. Meanwhile, a theoretical methodology for simulating the Coulomb explosion dynamics of small molecules was developed. This simulation methodology is fast, accurate enough, and very informative. The Coulomb explosion dynamics of 1,2-dichloroethene, methyl iodide, and thiophenone simulated using this methodology are shown and discussed in detail in this thesis. The simulation results are also compared with the experimental results for 1,2-dichloroethene and methyl iodide to reveal more details about the Coulomb explosion dynamics of these molecules, and the comparison finds both similarities and discrepancies between the experimental and the simulation results. The experimental and theoretical work on 1,2-dichloroethene shows that the angular distributions of the ion images are the only thing to distinguish the cis- and trans-isomers. The experimental and theoretical results for methyl iodide suggest that there could be intramolecular charge transfers during the dissociation. The results for the simulations of Coulomb explosion dynamics of thiophenone suggest that several significantly different structures along the (photo-induced) ring-opening reaction pathway of thiophenone can be distinguished by examining the simulated asymptotic speeds of fragment ions, suggesting that Coulomb explosion imaging is potentially a technique for investigating ring-opening dynamics of organic molecules.
Date of Award23 Sept 2022
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorMichael N R Ashfold (Supervisor) & Andrew J Orr-Ewing (Supervisor)

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