UvA

We are surrounded by carbon, even made of it. The ability of carbon to form multiple saturated and unsaturated bonds allows it to have a very rich chemistry. In fact, most of the larger molecules detected in space contain carbon. Moreover, towards many phases of stellar evolution, telescopes observe distinct infrared emission features named aromatic infrared bands (AIBs) that originate from Polycyclic Aromatic Hydrocarbons (PAHs). In this thesis studies are reported that address key aspects of the identification of these PAHs as well as their ‘rise and fall’.
Analysis of the afore mentioned emission spectra indicates that a small set of particularly stable, large and compact PAHs referred to as grandPAHs dominate the PAH population. So far, the intrinsic properties of grandPAHs under astronomically relevant conditions -clearly crucial for interpreting AIBs- have remained out of reach. In my studies I have used laser desorption to bring non-volatile molecules into the gas phase under astronomically relevant conditions and the infrared-free-electron laser FELIX to characterize the infrared spectral features over a wide wavelength range. These studies provide a solid basis for astronomers to narrow down the hypothesized PAH population to more specific families.
As yet, there are many unresolved questions of the PAH formation chemistry. As a result, densities of PAHs in the interstellar medium are consistently underestimated. In this thesis major insight has been obtained on this by identifying with mass-selective infrared spectroscopy the discharge reaction products of two simple aromatic molecules.
Finally, the unique advantages of infrared spectroscopy to determine the structure of weakly bound complexes has been employed to study how PAHs interact with other PAHs by π-π stacking and how PAHs interact with water. Both interactions are crucial for understanding the chemistry of PAHs under non-isolated conditions such as occurring in interstellar dust grains. Apart from linking the gaseous and solid form of carbon in the universe, also supramolecular chemistry, materials science and biochemistry benefit from a detailed understanding of these intermolecular, non-covalent interactions.
Christmas 2021 marks the launch of the James Webb Space Telescope, a unique observation platform that is expected to revolutionize our understanding of the Universe. The interpretation of the observations that will be made with this instrument is critically dependent on laboratory studies. The present thesis forms in this respect an important contribution to the body of knowledge needed to come to a consistent interpretation.