TY - BOOK
T1 - Time-resolved Photoionization Studies of Polyatomic Molecules
AU - Bjørnholst, Martin Alex
PY - 2018
Y1 - 2018
N2 - Non-adiabatic transitions are central in the study of photoinduced dynamics of polyatomic molecules. Time-resolved photoelectron spectroscopy (trpes) is a technique that is particularly sensitive to the changes in electronic structure and thus non-adiabatic transitions between electronically excited states have been revealed in a vast number of molecules by trpes studies. The non-radiative molecular response to excitation, e. G. Internal conversion (ic), is often found to occur on the ultrafast timescale. The associated strong nonadiabatic couplings occur only along a small subset of nuclear degrees of freedom and few structural changes are inherently responsible for the ultrafast ic. The link between molecular structure and the excited state structural changes has previously been conceptualised as dynamophores. The vuv photoinduced dynamics of four cyclic ketones and one linear ketone is studied and exhibit qualitatively similar dynamics. The initially excited states have 3d rydberg character but also display partial (, pi) valence character. The observed excited state lifetimes are quantitatively similar, indicating that a common deactivation mechanism is associated with 3d rydberg excitation in ketones and as such the dynamics are consistent with the dynamophore concept. The ring-opening and dissociative dynamics of cyclopropane is studied by a joint a computational and experimental study. The computational results show that vertical excitation energies are inadequate to predict and assign the experimental absorption spectrum. The explicit inclusion of the electromagnetic field associated with a pump pulse is required to qualitatively reproduce the absorption spectrum. The ensuing dynamics are also simulated and shows impressive quantitative agreement with the experimental results. Model systems for the disulfide bond and the peptide, which are both related to the structure of proteins are also investigated. The dynamics are similar in the sense that a dense manifold of rydberg states is present in both cases and these efficiently couple with valence states, ultimately leading to dissocation. Finally, the potential ultrafast intersystem crossing (isc) in three methylated benzene-derivatives is investigated computationally and the same structural change associated with ic is highlighted as being crucial to the potential isc as well in all three compounds, consistent with a common dynamophore in the systems.
AB - Non-adiabatic transitions are central in the study of photoinduced dynamics of polyatomic molecules. Time-resolved photoelectron spectroscopy (trpes) is a technique that is particularly sensitive to the changes in electronic structure and thus non-adiabatic transitions between electronically excited states have been revealed in a vast number of molecules by trpes studies. The non-radiative molecular response to excitation, e. G. Internal conversion (ic), is often found to occur on the ultrafast timescale. The associated strong nonadiabatic couplings occur only along a small subset of nuclear degrees of freedom and few structural changes are inherently responsible for the ultrafast ic. The link between molecular structure and the excited state structural changes has previously been conceptualised as dynamophores. The vuv photoinduced dynamics of four cyclic ketones and one linear ketone is studied and exhibit qualitatively similar dynamics. The initially excited states have 3d rydberg character but also display partial (, pi) valence character. The observed excited state lifetimes are quantitatively similar, indicating that a common deactivation mechanism is associated with 3d rydberg excitation in ketones and as such the dynamics are consistent with the dynamophore concept. The ring-opening and dissociative dynamics of cyclopropane is studied by a joint a computational and experimental study. The computational results show that vertical excitation energies are inadequate to predict and assign the experimental absorption spectrum. The explicit inclusion of the electromagnetic field associated with a pump pulse is required to qualitatively reproduce the absorption spectrum. The ensuing dynamics are also simulated and shows impressive quantitative agreement with the experimental results. Model systems for the disulfide bond and the peptide, which are both related to the structure of proteins are also investigated. The dynamics are similar in the sense that a dense manifold of rydberg states is present in both cases and these efficiently couple with valence states, ultimately leading to dissocation. Finally, the potential ultrafast intersystem crossing (isc) in three methylated benzene-derivatives is investigated computationally and the same structural change associated with ic is highlighted as being crucial to the potential isc as well in all three compounds, consistent with a common dynamophore in the systems.
UR - https://rex.kb.dk/primo-explore/fulldisplay?docid=KGL01011972648&context=L&vid=NUI&search_scope=KGL&tab=default_tab&lang=da_DK
M3 - Ph.D. thesis
BT - Time-resolved Photoionization Studies of Polyatomic Molecules
PB - Department of Chemistry, Faculty of Science, University of Copenhagen
ER -