Ph. D. Thesis: Ionization and Fragmentation of Complex Molecules and Clusters. Biomolecules and Polycyclic Aromatic Hydrocarbons
by
Henrik A. B. Johansson(Stockholm University, Department of Physics)
→
Europe/Stockholm
FB53
FB53
Description
This work deals with ionization and fragmentation of biomolecules and polycyclic aromatic
hydrocarbon (PAH) molecules. They are studied in the gas phase both as isolated molecules and
as weakly bound clusters. The purpose of the experimental and theoretical investigations are to
elucidate charge and energy transfer and related redistribution processes, as well as fragmentation
behaviors.
The first part of this thesis presents results from studies on biomolecular ions, in particular
nucleotides and peptides, which are primarily examined in electron capture induced dissociation
processes. These investigations are relevant for the better understanding of radiation damage
to DNA and processes involved in the sequencing of proteins. It is found that the immediate
environment have a decisive influence on the fragmentation behaviors. Evaporation of surrounding
molecules protect the biomolecules, but their effect on the electronic structure may also enhance
or suppress different fragmentation channels.
In the second part of the thesis, results from studies on PAH molecules are presented.
Experimentally, their properties are mainly probed through collisions with atomic ion projectiles
having kilo-electronvolt kinetic energies. As a widespread pollutant on Earth, and as a family
of abundant molecules in space, PAHs are not only relevant from an environmental and health
perspective, but they are also important for the understanding of the universe. The present results
relate to the stabilities of these molecules, both in isolated form and in clusters, when heated or
multiply ionized. It is found to be easier to remove several electrons from clusters of PAH molecules
than from isolated PAHs, and fission processes determine their ultimate stabilities. Heated lowcharge
state clusters of PAHs undergo long evaporation sequences once these have started. For
isolated and heated PAHs, internal structural rearrangements are demonstrated to be important in
the fragmentation processes.
