The electronic structure and deexcitation pathways of isolated biomolecular ions

The electronic structure of biomolecules is, in combination with the geometric structure, crucial for their functionality. However, the electronic structure is challenging to assess experimentally due to the high complexity of these large molecular systems. One strategy is to first determine the electronic structure of simpler biomolecular subunits and to increase the systems' complexity in further studies in a controlled manner. This bottomup approach also extends to the elimination of solvent molecules to rule out solventanalyte interactions. The work in this thesis focuses on the study of the intrinsic properties of two subunits of biomolecules, metalloporphyrins and ammonia derivatives which are found in amino acids. Metalloporphyrins have biological functions such as oxygen transport and light harvesting and find today, based on their electronic and optical properties, many industrial and medical applications. Amino acids are the building blocks of proteins which cover a variety of functions in living organisms. In this thesis, the electronic structure and the photofragmentation of these molecules are studied by ion yield spectroscopy in the VUV and soft X-ray energy region at 3rd generation synchrotron light sources. The nitrogen K-edge spectroscopic fingerprint of cationic ammonia derivatives NH${}_y^{+}$ (y = 0-3), used as a model of protonated amino groups in amino acids, is determined both experimentally and theoretically. This provides useful information for future studies on systems containing these chemical groups in a more complex environment. The local electronic structure of the metal center of an isolated metalloporphyrin is revealed by a novel experimental strategy, combining electrospray ionization tandem mass spectrometry with metal L-edge spectroscopy, supported by quantum-mechanical calculations. In addition, the measurement of the photo products allows to draw conclusions on the relaxation mechanisms after the metal inner-shell excitation, thereby disclosing an orbital-specific deexcitation. By employing VUV action spectroscopy, the valence electronic structure of isolated metalloporphyrins is assessed. The ionization energies of metalloporphyrin cations are determined and evidences for a non-statistical fragmentation of the metalloporphyrins after photoionization, in contrast to the photoexcitation case, are revealed.