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Rotational spectroscopy of nitrogen-containing radicals

Presentation #419.01 in the session Laboratory Astrophysics (LAD) Division Meeting: A Universe of Carbon III.

Published onJun 29, 2022
Rotational spectroscopy of nitrogen-containing radicals

Nitrogen-containing aromatic structures such as pyrrole, pyridine, purine, and pyrimidine comprise an important structural motif in biomolecules. Molecules containing these functional groups have been detected on meteorites with non-terrestrial isotopic abundances, but no such molecule has yet been unambiguously detected in space. Detailed formation mechanisms for nitrogen-containing aromatic molecules under astrophysically relevant conditions have not been fully elucidated, though the prevailing evidence suggests that radical chemistry in the gas phase and/or condensed phase plays a key role. Direct observation of the key radical intermediates, either in space or in reactive environments designed to simulate chemistry in space-like conditions, are needed to test this hypothesis. However, owing to their reactivity, radicals are challenging to generate and measure in the laboratory, and for many fundamental nitrogen-containing radicals little experimental data is available.

My group’s research uses a combination of Fourier transform microwave spectroscopy and ab initio quantum chemical calculations at the coupled cluster level to obtain high-resolution spectroscopic data for reactive molecules, including radicals. Recently, we have targeted several fundamental nitrogen-containing radicals that may serve as reactive intermediates in the formation of nitrogen-containing aromatic molecules: cyanovinyl, pyrrolyl, and pyridyl. Cyanovinyl has been proposed to react with vinyl cyanide to form pyridine, a prototypical 6-member nitrogen-containing aromatic ring, at temperatures relevant for interstellar clouds. Pyrrolyl and pyridyl are radical derivatives of nitrogen-containing aromatics which may play a role in the growth of larger polycyclic molecules. The rotational spectrum of two isomers of the cyanovinyl radical will be discussed, along with computational spectroscopy of pyrrolyl and pyridyl and a tentative detection of a pyridyl isomer. Results from this work provide new spectroscopic handles for experimental investigations of their reactivity and lay the foundation for searches for these species in interstellar clouds and star-forming regions.

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