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Astrophysics and Space Science

, Volume 240, Issue 1, pp 13–37 | Cite as

Cyanopolyyne chemistry in TMC-1

  • N. Winstanley
  • L. A. M. Nejad
Article

Abstract

Using pseudo-time-dependent models and three different reaction networks, a detailed study of the dominant reaction pathways for the formation of cyanopolyynes and their abundances in TMC-1 is presented. The analysis of the chemical reactions show that for the formation of cyanopolyynes there are two major chemical regimes. First, early times of less than ∼104 yrs when ion-molecule reactions are dominant, the main chemical route for the formation of larger cyanopolyynes is
$$C_n H^ + \xrightarrow{N}C_n N^ + \xrightarrow{{H_2 }}HC_n N^ + \xrightarrow{{H_2 }}H_2 C_n N^ + \xrightarrow{{e^ - }}HC_n N$$
wheren=5, 7, and 9. Second, at times greater than 104 yrs, when neutral-neutral reactions become dominant, two major reaction routes for the formation of cyanopolyynes are (a),
$$HCN\xrightarrow{{C_2 H}}HC_3 N\xrightarrow{{C_2 H}}HC_5 N\xrightarrow{{C_2 H}}HC_7 N\xrightarrow{{C_2 H}}HC_9 N$$
and (b)
$$C_n H_2 + CN \to HC_{n + 1} N + H,{\text{ }}n = 4,6, and 8$$

depending on the reaction network used. The results indicate that for route (a) large abundances ofC2H (fractional abundances of ∼10−7), and for route (b) large abundances ofC2H2 are required in order to reproduce the observed abundances of cyanopolyynes. The calculated abundances of cyanopolyynes show great sensitivity to the value of extinction particularly att≳5×105 yrs (i.e. photochemical timescale). The effect of other physical parameters, such as the cosmic-ray ionization abundances are also examined. In general, the model calculations show that the observed abundances of cyanopolyynes can be achieved by pseudo-time-dependent models at late times of several million years.

Keywords

Late Time Great Sensitivity Reaction Pathway Reaction Network Ionization Abundance 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Kluwer Academic Publishers 1996

Authors and Affiliations

  • N. Winstanley
    • 1
  • L. A. M. Nejad
    • 1
  1. 1.Department of Mathematics and PhysicsManchester Metropolitan UniversityManchester

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