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- Gatchell, Michael, 1988-
(author)
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Molecular Hole Punching : Impulse Driven Reactions in Molecules and Molecular Clusters
- 2016
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Doctoral thesis (other academic/artistic)abstract
- When molecules are excited by photons or energetic particles, they will cool through the emission of photons, electrons, or by fragmenting. Such processes are often thermal as they occur after the excitation energy has been redistributed across all degrees-of-freedom in the system. Collisions with atoms or ions may also lead to ultrafast fragmentation in Rutherford-like scattering processes, where one or several atoms can literally be knocked out of the molecule by the incoming projectile before the energy can be completely redistributed. The resulting fragmentation pathways can in such knockout processes be very different from those in thermal processes.This thesis covers extensive studies of collisions between ions/atoms and isolated Polycyclic Aromatic Hydrocarbon (PAH) molecules, isolated fullerene molecules, or clusters of these. The high stabilities and distinct fragmentation channels make these types of molecules excellent test cases for characterizing knockout-driven fragmentation and the reactions that these processes can lead to. I will present experimental measurements for a wide range of energies and compare them with my own molecular dynamics simulations and quantum chemical calculations. In this thesis, I present an in-depth study of the role of knockout in the energetic processing of molecules and clusters. The competition between knockout and thermally driven fragmentation is discussed in detail.Knockout-driven fragmentation is shown to result in exotic fragments that are far more reactive than the intact parent molecules or fragments from thermal processes. When such reactive species are formed within molecular clusters efficient molecular growth can take place on sub-picosecond timescales. The cluster environments are crucial here because they protect the newly formed molecules by absorbing excess energy. This is a possible pathway for the growth of large PAHs, fullerenes, and similar carbonaceous complexes found in, for instance, the interstellar medium.
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| 2. |
- Wolf, Michael, 1989-
(author)
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Energetic processing of complex molecules in the gas phase
- 2018
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Doctoral thesis (other academic/artistic)abstract
- Collisions between molecules and gas phase targets often lead to various intriguing processes. Such collisions may induce fragmentation of molecules that can be divided into different subsets depending on the projectile, target, and collision energy. One major part of the present research is the exploration of astrophysical relevant collision mechanisms. In collisions between polycyclic aromatic hydrocarbon (PAH) molecules or fullerenes with, for example, helium, nuclear stopping can lead to the prompt knockout of a carbon atom from the molecule. Such a vacancy in the molecular carbon backbone can be highly reactive, and lead to the formation of larger molecules. The energy dependencies of such processes are important for the understanding of astrochemical molecular growth processes, which in turn may lead to the formation of larger and more complex molecules in space. In addition, hydrogenation of PAHs changes their structures and internal properties, including their resistance against fragmentation. To better understand the effects of hydrogenation on the fragmentation of PAHs, low energy photofragmentation experiments are presented along with the collision experiments, and a detailed comparison is made between the effects of these different types of energy transfer processes.Besides astrophysically relevant research, studies on the response of biomolecules to collisions with gas phase targets are presented. Here, the energy dependence for formation of the protonated n-butyl β-ionone Schiff base through electrocyclization of the protonated n-butylamine Schiff base of all-trans-retinal in collisions is presented. The latter is a model compound for all-trans-retinal, the chromophore of the light sensitive opsin proteins, and such studies are essential for the understanding of the operation of mammal vision.While our collision studies are very successful, they are sometimes also limited by the experimental timescale. Therefore, we have constructed an experimental setup for ion storage and fragmentation analysis. The goal of this new experiment is to store internally hot fragments to investigate their behavior on extended timescales and as functions of internal excitation energies.
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