HC3N interstellar

CH3I (methyl iodide) principal axes, 103 If rotation, 113 CH2NH (methanimine) interstellar, 120 Cr203 (chromium trioxide) in alexandrite laser, 347ff in ruby laser, 346ff HC3N (cyanoacetylene) interstellar, 120 HCOOH (formic acid) interstellar, 120 NH2CN (cyanamide) interstellar, 120... 

Both of these approaches involve collisions of two large species. According to model calculations by one of us (Herbst 1983), neither of these syntheses can reproduce the observed high abundance of HC3N in sources such as the nearby dense interstellar Cloud TMC-1. However, this negative assessment for the first mechanism relies on a laboratory rate coefficient for reaction (3.39) at room temperature that shows the reaction to be slow slow ion-molecule reactions at room temperature often become more rapid at lower temperature (Rowe et al. 1984). Likewise, the negative assessment for the second mechanism is based on a theoretical calculation for the rate coefficient of the radiative association reaction. 

Fukuzawa, K. Osamura, Y. Molecular orbital study of neutral-neutral reactions concerning HC3N formation in interstellar space. Astrophys. J. 1997, 489, 113-121, and references therein. 

In this review we have attempted to show that the circumstellar envelopes of cool, late-type stars possess a rich chemistry which is similar in many respects to that occurring in interstellar clouds. In carbon-rich envelopes, cosmic-rays and ultraviolet photons drive a chemistry dominated by ion-molecule reactions and photo-reactions. Such a chemistry has been applied to the envelope of IRC-l-10216 and has been shown to reproduce the observations extremely well. In oxygen-rich envelopes these processes also occur but the presence of large amounts of OH make neutral chemistry more important. In both cases the effects of ion-dipolar collisions has little effect on abundances, with the exception of HC3N and some protonated species (Glassgold et al. 1987, Millar 1987, unpublished). 

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