Ph.D. Thesis: Photo-induced molecular processes and charge recombination reactions driven by non-adiabatic couplings
by
Michael Stenrup(Stockholm University, Department of Physics)
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Europe/Stockholm
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FA32
Description
This thesis is based on a number of theoretical studies of molecular processes in which
non-adiabatic effects play a crucial role. The main part is devoted to the photophysics and
photochemistry of five-membered aromatic heterocyclic compounds, with particular focus on
furan and thiophene. These species absorb light in the UV region of the spectrum, but exhibits
neither fluorescence nor phosphorescence. A plausible explanation for this is the presence of
very fast radiationless deactivation mechanisms that depopulate the excited states before emission
can occur. In the present thesis, several possible such mechanisms are considered based on the
results of static electronic structure calculations as well as mixed quantum-classical dynamics
simulations. A common feature of the investigated pathways is the presence of easily accessible
conical intersections (surface crossings) through which non-adiabatic population transfer to the
electronic ground state may take place. Also considered in the present work are the bond-breaking/
bond-forming processes that are expected to follow once the ground state has been reached.
Another prominent example of non-adiabatic processes is charge recombination reactions
involving either two oppositely charged ions or a cation and an electron. Here, the reactants
and products belong to different electronic states of the system as a whole and therefore a nonadiabatic
transition is necessary for the recombination to occur. Two such processes are considered
in the present thesis; mutual neutralization of oppositely charged hydrogen ions and dissociative
recombination of the formyl and iso-formyl cations. The cross sections (rate coefficients) and
underlying mechanisms of these reactions are investigated at a fully quantum mechanical level.