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Title:First Interstellar Detection Of Isocyanodiacetylene (hc4nc), The Largest Isocyanide Molecule In The Ism
Author(s):Xue, Ci
Contributor(s):McGuire, Brett A.; Lee, Kelvin; Burkhardt, Andrew M.; Loomis, Ryan A; Remijan, Anthony; Herbst, Eric; Willis, Eric R.
Abstract:The cyanide and isocyanide (-\chem{CN} and -\chem{NC}) pairs of isomers have been used regularly to probe the physical conditions and history of interstellar sources and to improve the accuracy and predictive power of astrochemical models. Two examples are the strong sensitivity of the $\chem{HCN}$/$\chem{HNC}$ abundance ratio to the gas kinetic temperatures\footnote{A. Hacar, A. D. Bosman, and E. F. van Dishoeck, A\&A 635, A4(2020)} and the dependence of the $\chem{CH_3CN}$/$\chem{CH_3NC}$ abundance ratio to the cosmic-ray ionization rates\footnote{E. R. Willis, et al., A\&A, 636, A29 (2020)}. Yet, despite the numerous detections of cyanides in astronomical environments, there have been very few confirmed detections of isocyanides. Alongside $\chem{C_nH_{2n+1}CN}$, one of the most frequently observed families of cyanide species in cold sources are the cyanopolyynes ($\chem{HC_{2n}CN}$). In contrast to their ubiquity, the only isocyanide version that had been successfully detected is $\chem{HCCNC}$, the isomer of $\chem{HC_3N}$. In this talk, we will present the first astronomical detection of the largest isocyanide molecule, isocyanodiacetylene ($\chem{HC_4NC}$), using the data available from the GOTHAM (Green Bank Telescope Observations of TMC-1: Hunting for Aromatic Molecules) observational program of TMC-1\footnote{B. A. McGuire, et al., ApjL, 900, L10 (2020)}. Assisted by a cutting-edge application of spectral line stacking and matched filtering techniques, we determined the \chem{NC}/\chem{CN} isomeric intensity ratios of the $\chem{HC_{2n}NC}$/$\chem{HC_{2n}CN}$ family rigorously for n=1 and 2 toward TMC-1 and provided an upper limit of that for n=3. The abundance ratios derived from observations helped in constraining the interplay between -\chem{CN} and -\chem{NC} formation chemistry and their dependence on the physico-chemical history of the source. This work also demonstrated the need for a detailed investigation of the related formation pathways in the laboratory.
Issue Date:2021-06-22
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Date Available in IDEALS:2021-09-24

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