2005/06/21 by Anthony J. Remijan, J. M. Hollis, F. J. Lovas +3 · 1 citation
Chemistry · Physics and Astronomy · #Advanced Chemical Physics Studies #Astrophysics #Astrophysics and Star Formation Studies #Chemical physics #Chemistry #Cyanide #Interstellar medium #Isocyanide #Materials science #Molecular Spectroscopy and Structure #Molecule #Organic chemistry #Photochemistry #Physics #astro-ph
paper · pdf · doi:10.1086/432908
published as Astrophys.J.632:333-339,2005 · 17 pages, 2 figures, accepted to the Astrophysical Journal
arxiv created 2005/06/21 · openalex publication_date 2005/10/03 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
We present strong detections of methyl cyanide (CH 3 CN), vinyl cyanide (CH 2 CHCN), ethyl cyanide (CH 3 CH 2 CN), and cyanodiacetylene (HC 4 CN) molecules with the Green Bank Telescope (GBT) toward the Sgr B2(N) molecular cloud. Attempts to detect the corresponding isocyanide isomers were only successful in the case of methyl isocyanide (CH 3 NC) for its J K = 1 0 -0 0 transition, which is the first interstellar report of this line. To determine the spatial distribution of CH 3 NC, we used archival Berkeley-Illinois-Maryland Association (BIMA) array data for the J K = 4 K -3 K ( K = 0-3) transitions, but no emission was detected. From ab initio calculations, the bonding energy difference between the cyanide and isocyanide molecules is >8500 cm -1 (>12,000 K). Thus, cyanides are the more stable isomers and would likely be formed more preferentially over their isocyanide counterparts. That we detect CH 3 NC emission with a single antenna (Gaussian beam size Ω B = 1723 arcsec 2 ) but not with an interferometer (Ω B = 192 arcsec 2 ) strongly suggests that CH 3 NC has a widespread spatial distribution toward the Sgr B2(N) region. Other investigators have shown that CH 3 CN is present both in the LMH hot core of Sgr B2(N) and in the surrounding medium, while we have shown that CH 3 NC appears to be deficient in the LMH hot core. Thus, large-scale, nonthermal processes in the surrounding medium may account for the conversion of CH 3 CN to CH 3 NC, while the LMH hot core, which is dominated by thermal processes, does not produce a significant amount of CH 3 NC. Ice analog experiments by other investigators have shown that radiation bombardment of CH 3 CN can produce CH 3 NC, thus supporting our observations. We conclude that isomers separated by such large bonding energy differences are distributed in different interstellar environments, making the evaluation of column density ratios between such isomers irrelevant unless it can be independently shown that these species are cospatial.