Computational characterization of photoionization and fragmentation processes of aminobenzoic acids

In this doctoral thesis, the fragmentation processes and spectroscopic features of aminobenzoic acids were studied using the methods of computational physics. Spectroscopy is a field of physics that studies the interactions between light and matter. The fundamental structure of matter is challenging to investigate, because molecules and atoms (and especially their constituent parts) are to small for direct visual inspection. The properties of matter can however be studied indirectly with spectroscopic methods. Sufficiently energetic radiation, such as ultraviolet radiation and x-rays, can ionize matter, that is, remove electrons from it through the absorption of photons. By studying the ionization processes we can investigate the structure and chemical properties of matter.

In this thesis the three isomers of aminobenzoic acid were studies using ionizing radiation from a synchrotron light source. The lower energy ultraviolet radiation (~10 eV photon energy) was used to ionize valence electrons, and x-rays (~300 eV photon energy) were used to ionize core electrons. The experiments revealed interesting differences in electronic structures and fragmentation products between the three isomers. The experimental results of spectroscopic measurements are complicated and their interpretation is very difficult, and often impossible, without theoretical modeling of the system. The prevailing physical theory on the atomic and molecular scale is quantum physics. Quantum chemical calculations however are very burdensome and in practice they are carried out on supercomputers with specialized software. In this work a wide range of computational quantum chemistry methods were used to characterize the system under investigation. With the help of quantum chemical modeling the experimental measurements could be interpreted and the differences between the isomers explained.