Detection of Interstellar HC<sub>4</sub>NC and an Investigation of Isocyanopolyyne Chemistry under TMC-1 Conditions
Ci Xue, Eric R. Willis, Ryan A. Loomis, Kin Long Kelvin Lee, Andrew M. Burkhardt, Christopher N. Shingledecker, Steven B. Charnley, Martin A. Cordiner, Sergei Kalenskii, Michael C. McCarthy, Eric Herbst, Anthony J. Remijan, Brett A. McGuire
Abstract
Abstract 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 σ . The total column density and excitation temperature of HC 4 NC are determined to be cm −2 and , respectively, using Markov chain Monte Carlo 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.