Imaging Photoinduced Dynamics in Gas-Phase Molecules Using Ultrafast Electron and X-ray Diffraction
Thesis Defense
1:00 pm –
3:00 pm
Jorgensen Hall Room: 207
Target Audiences:
Contact:
Physics Department, (402) 472-2770, paoffice2@unl.edu
Sri Bhavya Muvva will defend her thesis in person.
Abstract: Investigating ultrafast structural changes in photoexcited molecules provides essential information on their governing reaction mechanisms and product formation. Time-resolved electron and X-ray diffraction are crucial techniques for capturing the structural information of photoexcited molecules on femtosecond timescales. Using ultrafast electron and X-ray diffraction experiments, we studied photoinduced dynamics in gas-phase molecules.
Photoexcitation of conjugated diene molecules with Ultraviolet (UV) laser pulses can lead to different reaction mechanisms, depending on their double bonds’ position and molecular rigidity. We investigated the time-resolved UV-induced excited-state structural dynamics of cis,cis-1,3-cyclooctadiene, an eight-membered cyclic conjugated diene molecule, using mega-electron-volt ultrafast electron diffraction (MeV-UED) experiment. This experiment was conducted at the MeV-UED facility of SLAC National Accelerator Laboratory. Combining results from the experiment and theoretical simulations, we explained the structural changes in this molecule from its first excited state to the ground state through a conical intersection (CI) seam. We identified a new reaction coordinate of ring distortion motion as the primary reaction coordinate of the nuclear motion from the Franck-Condon region to the CI seam.
Identifying dissociation pathways and tracking structural changes along the existing pathways of photodissociation reactions is crucial to understanding their photochemistry and is often challenging in many chemical reactions. Using time-resolved X-ray scattering experiment, we investigated the UV photodissociation dynamics of diiodomethane molecules. The experiment was performed using the Coherent X-ray Imaging (CXI) instrument at the Linac Coherent Light Source (LCLS). A comparison of the experimental diffraction signals with the simulated diffraction signals shows a good qualitative match. The major dissociation pathway of this UV-induced dissociation reaction and the structural changes taking place along this channel are identified from our results.
Gas-phase diffraction studies of low-vapor-pressure molecules require a specialized sample delivery system. Dicyclopentadiene molecules have a low vapor pressure. Strong field ionization of dicyclopentadiene induces a retro-Diels-Alder reaction, yielding cyclopentadiene. Examining the structural dynamics of this process provides insights into its reaction mechanisms. Using our KeV-UED setup, we recorded the diffraction patterns of dicyclopentadiene molecules. Sample delivery details and diffraction results for these molecules are presented.
Abstract: Investigating ultrafast structural changes in photoexcited molecules provides essential information on their governing reaction mechanisms and product formation. Time-resolved electron and X-ray diffraction are crucial techniques for capturing the structural information of photoexcited molecules on femtosecond timescales. Using ultrafast electron and X-ray diffraction experiments, we studied photoinduced dynamics in gas-phase molecules.
Photoexcitation of conjugated diene molecules with Ultraviolet (UV) laser pulses can lead to different reaction mechanisms, depending on their double bonds’ position and molecular rigidity. We investigated the time-resolved UV-induced excited-state structural dynamics of cis,cis-1,3-cyclooctadiene, an eight-membered cyclic conjugated diene molecule, using mega-electron-volt ultrafast electron diffraction (MeV-UED) experiment. This experiment was conducted at the MeV-UED facility of SLAC National Accelerator Laboratory. Combining results from the experiment and theoretical simulations, we explained the structural changes in this molecule from its first excited state to the ground state through a conical intersection (CI) seam. We identified a new reaction coordinate of ring distortion motion as the primary reaction coordinate of the nuclear motion from the Franck-Condon region to the CI seam.
Identifying dissociation pathways and tracking structural changes along the existing pathways of photodissociation reactions is crucial to understanding their photochemistry and is often challenging in many chemical reactions. Using time-resolved X-ray scattering experiment, we investigated the UV photodissociation dynamics of diiodomethane molecules. The experiment was performed using the Coherent X-ray Imaging (CXI) instrument at the Linac Coherent Light Source (LCLS). A comparison of the experimental diffraction signals with the simulated diffraction signals shows a good qualitative match. The major dissociation pathway of this UV-induced dissociation reaction and the structural changes taking place along this channel are identified from our results.
Gas-phase diffraction studies of low-vapor-pressure molecules require a specialized sample delivery system. Dicyclopentadiene molecules have a low vapor pressure. Strong field ionization of dicyclopentadiene induces a retro-Diels-Alder reaction, yielding cyclopentadiene. Examining the structural dynamics of this process provides insights into its reaction mechanisms. Using our KeV-UED setup, we recorded the diffraction patterns of dicyclopentadiene molecules. Sample delivery details and diffraction results for these molecules are presented.