| الوصف: |
The interactions between light and matter are ubiquitous in the universe and initiate many fundamental chemical processes, such as photosynthesis and vitamin D production. Therefore, gaining a better understanding of how light interacts with molecules and how light-induced reaction mechanisms develop from reactants to products is of great interest. This work uses a velocity-map imaging time-of-flight spectrometer to study the unimolecular photodissociation dynamics of molecules in the gas phase. The observables of the experiment are the product scattering distributions, which are a fingerprint of the chemical reaction, and the product time-of-flight, which reveals the fragment identities. The experiments aim to understand which chemical bonds break, how the system evolves on the potential energy surfaces involved in the reaction, and how the available energy is distributed over the product degrees of freedom. The first part of this thesis studies the photodissociation of tetrahydrofuran at 193 nm, N,N-dimethylformamide at 225 nm and 245 nm, and the N,N-dimethylformamide cation at 225nm, 245nm, and 280nm. Tetrahydrofuran is a model for the DNA backbone molecule ribose, and N,N-dimethylformamide is a model for the peptide bond, which forms the backbone of proteins. Both molecules reveal complex dissociation dynamics, in which population transfer to lower electronic states is possible after the initial excitation. This population transfer probably plays an important role in the photoprotection of molecules in biological species. The great majority of the available energy is distributed into the internal product modes rather than product kinetic energy. This observation is pronounced in the N,N-dimethylformamide cation study, in which a change in photon energy of more than 0.5 eV leads to the same product kinetic energy release. The second part of the thesis describes the design and characterization of a novel femtosecond laser beamline to the experiment which allows us to conduct Coulomb explosion imaging ... |