Large molecules in the envelope surrounding IRC+10216

Abstract

A new chemical model of the circumstellar envelope surrounding the carbon-rich star IRC110216 is developed that includes carbon-containing molecules with up to 23 carbon atoms. The model consists of 3851 reactions involving 407 gas-phase species. Sizeable abundances of a variety of large molecules ± including carbon clusters, unsaturated hydrocarbons and cyanopolyynes ± have been calculated. Negative molecular ions of chemical formulae C 2 n and C n H 2 7 # n # 23 exist in considerable abundance, with peak concentrations at distances from the central star somewhat greater than their neutral counterparts. The negative ions might be detected in radio emission, or even in the optical absorption of background field stars. The calculated radial distributions of the carbon-chain C n H radicals are looked at carefully and compared with interferometric observations.

The UMIST database for astrochemistry 2012

“…A36, page 8 of 13 Table 5 of Millar et al (2000); (2) Bakker et al (1997); (3) The carbon-chain oxide, C 3 O, is assumed to originate via the recombination of H 3 C 3 O + and H 2 C 3 O + in Rate12 and CM09. However, the production of H 3 C 3 O + is much more rapid in Rate12 due to the inclusion of the radiative association reaction,…”

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Photodissociation and chemistry of N2in the circumstellar envelope of carbon-rich AGB stars

“…be found in Millar et al (2000) and Cordiner & Millar (2009). Improvements in the model are summarised in Sect.…”

Chemistry in the circumstellar medium

“…The recent detection of C 6 H − in IRC+10216 by McCarthy et al (2006), was predicted implicitly by the calculations of Millar et al (2000) who predicted anion/neutral ratios of between 0.01 and 0.4 based on efficient formation through radiative electron attachment, which occurs when the neutral has six or more atoms, and destruction mainly through photodissociation. Detailed calculations by Millar et al (2007) show that anions as small as C 4 H − should be detectable in IRC+10216.…”