Interstellare aminosyre-prekursorer studert med mikrobølgespektroskopi og kvantekjemiske beregninger

Abstract

The main objective of the work for this thesis was to establish the foundation for detection of the amino acid precursor Z-3-amino-2-propenenitrile in interstellar space. Detection of compounds in interstellar space is usually done via observation of rotational emission spectra, and in this work the microwave spectra of Z-3-amino-2-propenenitrile and of three vibrationally excited states were assigned. The spectra of four of its isotopologues were also assigned, and a so-called substitution structure was derived from these spectra and from spectra assigned by our collaborators. The substitution structure was found to be unreliable, because three atoms were lying close to the principal axis. A structural analysis of Z-3-amino-2-propenenitrile was carried out using ab initio calculations. It was found that Z-3-amino-2-propenenitrile was the most thermodynamical favourable isomer. Analysis of rotational barriers and bond lengths predicted that Z-3-amino-2-propenenitrile had a high degree of conjugation. The conjugation was probably caused by an intramolecular electrostatic interaction involving a hydrogen atom, or an interaction between opposite bond moments. The calculations also predicted that this isomer was nearly planar.

Due to the extraordinary low temperatures in interstellar space, with temperatures as low as 10 K, it was also of interest to investigate the mechanism leading to the formation of 3-amino-2-propenenitrile from ammonia and cyanoacetylene. A gas phase reaction mechanism was modelled with G3-theory. A mechanism which was consistent with catalytic formation of the compound at standard conditions was proposed. It was found that it is not likely that this reaction can occur in the cold parts of interstellar clouds, so a similar mechanism with protonated cyanoacetylene was investigated. The activation energy for this reaction was significantly lower, but as it was found that ammonia had the highest proton affinity of the reactants, this mechanism is supposed to be a minor channel to the formation of 3-amino-2-propenenitrile in interstellar space.