Detection of Interstellar HC$_4$NC and an Investigation of Isocyanopolyyne Chemistry under TMC-1 Conditions. (arXiv:2008.12345v1 [astro-ph.GA])

Detection of Interstellar HC$_4$NC and an Investigation of Isocyanopolyyne Chemistry under TMC-1 Conditions. (arXiv:2008.12345v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Xue_C/0/1/0/all/0/1">Ci Xue</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Willis_E/0/1/0/all/0/1">Eric R. Willis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Loomis_R/0/1/0/all/0/1">Ryan A. Loomis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lee_K/0/1/0/all/0/1">Kin Long Kelvin Lee</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Burkhardt_A/0/1/0/all/0/1">Andrew M. Burkhardt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shingledecker_C/0/1/0/all/0/1">Christopher N. Shingledecker</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Charnley_S/0/1/0/all/0/1">Steven B. Charnley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cordiner_M/0/1/0/all/0/1">Martin A. Cordiner</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kalenskii_S/0/1/0/all/0/1">Sergei Kalenskii</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McCarthy_M/0/1/0/all/0/1">Michael C. McCarthy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Herbst_E/0/1/0/all/0/1">Eric Herbst</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Remijan_A/0/1/0/all/0/1">Anthony J. Remijan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McGuire_B/0/1/0/all/0/1">Brett A. McGuire</a>

We report an astronomical detection of HC$_4$NC for the first time in the
interstellar medium with the Green Bank Telescope toward the TMC-1 molecular
cloud with a minimum significance of $10.5 sigma$. The total column density
and excitation temperature of HC$_4$NC are determined to be
$3.29^{+8.60}_{-1.20}times 10^{11}$ cm$^{-2}$ and $6.7^{+0.3}_{-0.3}$ K,
respectively, using the MCMC analysis. In addition to HC$_4$NC, HCCNC is
distinctly detected whereas no clear detection of HC$_6$NC is made. We propose
that the dissociative recombination of the protonated cyanopolyyne,
HC$_5$NH$^+$, and the protonated isocyanopolyyne, HC$_4$NCH$^+$, are the main
formation mechanisms for HC$_4$NC while its destruction is dominated by
reactions with simple ions and atomic carbon. With the proposed chemical
networks, the observed abundances of HC$_4$NC and HCCNC are reproduced
satisfactorily.

We report an astronomical detection of HC$_4$NC for the first time in the
interstellar medium with the Green Bank Telescope toward the TMC-1 molecular
cloud with a minimum significance of $10.5 sigma$. The total column density
and excitation temperature of HC$_4$NC are determined to be
$3.29^{+8.60}_{-1.20}times 10^{11}$ cm$^{-2}$ and $6.7^{+0.3}_{-0.3}$ K,
respectively, using the MCMC analysis. In addition to HC$_4$NC, HCCNC is
distinctly detected whereas no clear detection of HC$_6$NC is made. We propose
that the dissociative recombination of the protonated cyanopolyyne,
HC$_5$NH$^+$, and the protonated isocyanopolyyne, HC$_4$NCH$^+$, are the main
formation mechanisms for HC$_4$NC while its destruction is dominated by
reactions with simple ions and atomic carbon. With the proposed chemical
networks, the observed abundances of HC$_4$NC and HCCNC are reproduced
satisfactorily.

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