Unlocking the Key to Life: Observation and Formation of Nitriles in Protoplanetary Disks

The chemical composition of protoplanetary disks around young stars affects the chemical habitability of nascent planets. Nitriles are key participants in reactions that lead to pre-biotically interesting molecules such as RNA and amino acids. However, their abundances and formation mechanisms in planet-forming disks are not well constrained. In this thesis, we present the first detection of ortho- CH₂CN in a protoplanetary disk. An excitation analysis reveals a disk-averaged column density (Ntot) of 4.7(± 0.4)*10^(12) cm^(−2), and a rotational temperature (Trot) of 38 ± 5 K. A radially resolved analysis shows that the CH₂CN column density peaks within the first 50 au of the disk whereas the Trot remains constant across the disk. Our observations and models point to a close chemical relationship between CH₂CN and the more commonly observed CH₃CN. We then investigate the role of VUV irradiation in nitrile formation by laboratory experiments. We irradiate NH₃:C₂H₆, NH₃:C₂H₄, and NH₃:C₂H₂ ice mixtures at 30 K, 40 K, and 50 K. We find that CH₃CN is formed in a subset of these experiments and that CH₃CH=NH is an intermediate for CH₃CN production. These reactions show a temperature dependence and sensitivity to the unsaturation of the hydrocarbon reactant. Comparison of our findings to observed molecule abundances in clouds suggests that these are not the main pathways for nitrile formation in disks. Contribution from ice chemistry involving the more abundant N₂ should be investigated.