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Titel:Development of low-scaling methods for the description of vibronic transitions and application in gas-phase ion chemistry
Autor:Marquardt, Sabrina
Weitere Beteiligte: Berger, Robert (Prof. Dr.)
Veröffentlicht:2018
URI:https://archiv.ub.uni-marburg.de/diss/z2019/0097
DOI: https://doi.org/10.17192/z2019.0097
URN: urn:nbn:de:hebis:04-z2019-00973
DDC: Chemie
Titel (trans.):Entwicklung niedrig-skalierender Methoden zur Beschreibung vibronischer Übergänge und Anwendung in der Gasphasen-Ionenchemie
Publikationsdatum:2019-10-16
Lizenz:https://rightsstatements.org/vocab/InC-NC/1.0/

Dokument

Schlagwörter:
NRMS, Theoretische Chemie, Vibronische Übergänge, Laserkühlung, Vibronic transitions, Quantenchemie, Massenspektrometrie, Rückstoßimpulsspektroskopie, NRMS

Summary:
Theoretical methods are developed and applied in relation to three gas phase experiments: Neutralization Reionization Mass Spectrometry (NRMS), laser cooling and Cold Target Ion Momentum Spectroscopy (COLTRIMS). All three are important techniques in gas phase ion chemistry research and can be described using similar theoretical models: The molecules under investigation undergo electronic transitions from an initial electronic state to a final electronic state and may at the same time also change their vibrational quantum number. Those vibronic transitions are in the Franck-Condon limit described with Franck-Condon factors (FCFs) which modulate the probability of the different electronic transitions. Whereas in NRMS state transitions are used to generate highly reactive molecular species from stable precursors, laser cooling achieves translational cooling of molecules by repeated electronic transitions and COLTRIMS provides information on electronic and geometrical structure. In this work a time-dependent generating function ansatz for the calculation of FCFs by Huh [PhD thesis, Johann Wolfgang Goethe-Universität Frankfurt am Main, 2010] is extended in order to calculate vibrational population distributions in the final state after one or several subsequent vibronic transitions. The calculated trajectories are discontinuous in some cases, which makes it necessary to implement algorithmic changes to the former developments. The method is applied to the molecule HNSi and combined with reaction rate calculations within the Statistical Adiabatic Channel Model (SACM) to predict signals in the mass spectrum. The results are compared to NRMS experiments. An extended version of the developed method is discussed which includes the description of a laser excitation with specific frequency. It is applied to a system with one vibrational degree of freedom in a laser cooling cycle. In the year 2013 Pitzer et al. [Science 2013, 341 (6150), 1096 1100] have shown that direct assignment of the absolute configuration for the molecule CHBrClF is possible with COLTRIMS. In this dissertation experimental data from synchrotron experiments in the year 2016 by Pitzer et al. [Chem. Phys. Chem. 2016, 17, 24652472] are analysed. The uncertainty of their evaluation due to the presence of different isotopes is discussed. Equilibrium structures and stabilities of multiply charged cations of CHBrClF are determined with quantum chemical methods. Furthermore, the fragmentation pathways of singly charged CDBrFI are investigated and calculated appearance energies are compared to experimental values. This work describes methods for the prediction and analysis of three gas phase experiments that involve vibronic transitions. These theoretical approaches integrate different advantages: The methods developed or applied herein are predominantly of quantum mechanical type, which have inherently high accuracy. The algorithms implemented and the approaches used are computationally efficient as they avoid for instance to explicitly count vibronic transitions or to perform optimizations with overly expensive quantum chemical methods. The methods are versatilely applicable to diverse molecules in different gas phase experiments. Furthermore, this dissertation contributes to the further development of the promising COLTRIMS method for the direct determination of absolute configuration.


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