Formation and photostability of N-heterocycles in space. I. The effect of nitrogen on the photostability of small aromatic molecules

Details Formation and photostability of N-heterocycles in space. I. The effect of nitrogen on the photostability of small aromatic molecules Formation and photostability of N-heterocycles in space. I. The effect of nitrogen on the photostability of small aromatic molecules

Apr 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005a%26a...433..583p&link_type=abstract

Astronomy and Astrophysics, Volume 433, Issue 2, April II 2005, pp.583-590

Biology

18

Astrobiology, Methods: Laboratory, Stars: Individual: Crl 618

Scientific paper

Nitrogen-containing cyclic organic molecules (N-heterocycles) play important roles in terrestrial biology, for example as the nucleobases in genetic material. It has previously been shown that nucleobases are unlikely to form and survive in interstellar and circumstellar environments. Also, they were found to be unstable against ultraviolet (UV) radiation. However, nucleobases were detected in carbonaceous meteorites, suggesting their formation and survival is possible outside the Earth. In this study, the nucleobase precursor pyrimidine and the related N-heterocycles pyridine and s-triazine were tested for UVstability. All three N-heterocycles were found to photolyse rapidly and their stability decreased with an increasing number of nitrogen atoms in the ring. The laboratory results were extrapolated to astronomically relevant environments. In the diffuse interstellar medium (ISM) these N-heterocycles in the gas phase would be destroyed in
10-100years, while in the Solar System at 1AU distance from the Sun their lifetime would not extend beyond several hours. The only environment where small N-heterocycles could survive, is in dense clouds. Pyridine and pyrimidine, but not s-triazine, could survive the average lifetime of such a cloud. The regions of circumstellar envelopes where dust attenuates the UVflux, may provide a source for the detection of N-heterocycles. We conclude that these results have important consequences for the detectability of N-heterocycles in astronomical environments.

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