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Simulations of branched carbon-chain chemistry in star-forming regions

Published online by Cambridge University Press:  04 September 2018

Robin T. Garrod
Robin T. Garrod*
Affiliation:
Depts. of Chemistry & Astronomy, University of Virginia, Charlottesville, VA 22904, USA email: [email protected]
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Abstract

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The detection of iso-propyl cyanide (i-C3H7CN) toward the Galactic Center hot-core source Sgr B2(N) (by Belloche et al. 2014) marked the first interstellar detection of an aliphatic molecule with a branched carbon-chain structure. Surprisingly, this branched form was found to have an almost equal abundance with its straight-chain homologue, normal-propyl cyanide (i:n = 0.40 ± 0.06). The detection of this first example of an interstellar molecule with a side-chain raises the question as to how prominent such structures may be in interstellar chemistry, and whether the large branched-to-straight chain ratio is maintained for even larger molecules.

Here are presented recently published models that simulate the chemistry occurring in Sgr B2(N) using a chemical network that explicitly includes the straight-chain and branched forms of propyl cyanide (normal/iso) and butyl cyanide (normal/iso/sec/tert), as well as butane (n/i) and pentane (n/i/neo). Formation is assumed to occur on dust-grain surfaces, but a full complement of destruction mechanisms is included both on the grains and in the gas phase.

The models suggest that branched structures become increasingly dominant as molecular sizes increase. In the case of butyl cyanide, the sec form is at least ∼2 times more abundant than the straight-chain normal form, and together the branched forms dominate normal-butyl cyanide by a factor of at least 3. The results for the larger alkanes suggest similarly large ratios of branched to straight-chain molecules. A key set of reactions in the surface/ice chemistry of interstellar nitriles is found to be the addition of the CN radical to unsaturated hydrocarbons, especially acetylene and ethene. The models also predict that the dominant, sec form of butyl cyanide reaches a peak abundance equal to that of n-propyl cyanide, albeit with a smaller emission radius. This makes s-C4H9CN a good candidate for detection. New ALMA observations to search for this molecule are ongoing.

Keywords

astrochemistryISM: abundancesISM: individual (Sagittarius B2N)ISM: moleculesmolecular processes
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 13 , Symposium S332: Astrochemistry VII: Through the Cosmos from Galaxies to Planets , March 2017 , pp. 403 - 408
Copyright
Copyright © International Astronomical Union 2018 

References

Belloche, A., Garrod, R. T., Müller, H. S. P., Menten, K. M., Comito, C. & Schilke, P. 2009 A&A, 499, 215Google Scholar
Belloche, A., Garrod, R. T., Müller, H. S. P. & Menten, K. M. 2014 Science, 345, 1584Google Scholar
Cami, J., Bernard-Salas, J., Peeters, E., & Malek, S. E. 2010 Science, 659, 1180–1182Google Scholar
Garrod, R. T. & Herbst, E. 2006 A&A, 457, 927Google Scholar
Garrod, R. T. 2013 ApJ, 765, 60Google Scholar
Garrod, R. T., Belloche, A., Müller, H. S. P. & Menten, K. M. 2017 ApJ, 601 A48Google Scholar
Marcelino, N., Cernicharo, J., Agúndez, M., Roueff, E., Gerin, M., Martín-Pintado, J., Mauersberger, R. & Thum, C. 2007 ApJ, 665, L127–L130Google Scholar