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Interstellar Isomers: The Importance of Bonding Energy Differences



A J. Remijan, J M. Hollis, Francis J. Lovas, David F. Plusquellic, P R. Jewell


We present new observations of large cyanide molecules and their corresponding isocyanide isomers toward the Sgr B2(N)molecular cloud. We report the first detection of the JK=10-00 transition of methyl isocyanide (CH3NC) with the 100-m Green Bank Telescope (GBT). Also, we detected strong emission from methyl cyanide (CH3CN), vinyl cyanide (CH2CHCN), ethyl cyanide (CH3CH2CN) and cyanodiacetylene (HC4CN) with the GBT. In order to determine the spatial distribution of CH3NC, we used archival BIMA array data of the JK=4K-3K (K=0-3) transitions but no emission was detected greater than the 1 sigma limit. From ab initio calculations, the bonding energy difference between cyanide and isocyanide molecules is >8500 cm-1 (>12,000 K). Thus, cyanides are the more stable isomers and would likely be formed preferentially than their isocyanide counterparts. Since we detect CH3NC emission with a single antenna (OB=1723 arcsec2) but not with an interferometer (OB=192 arcsec2), this strongly suggests that CH3NC has a widespread spatial distribution toward the Sgr B2(N) region. Other investigators have shown that CH3CN is present both in the LMH hot core and the surrounding medium, while we have shown that CH3NC appears to be deficient in the LMH hot core. Thus, large-scale, non-thermal processes in the surrounding medium may account for the conversion of CH3CN to CH3NC while the LMH hot core, which is dominated by thermal processes, does not produce a significant amount of CH3NC. Ice analog experiments by other investigators have shown that radiation bombardment CH3CN of can produce CH3NC, thus tending to support what is observed. We conclude that isomers sepa
Astrophysical Journal


bonding energy, cyanides, interstellar molecules, isocyanides, isomers, radioastromomy


Remijan, A. , Hollis, J. , Lovas, F. , Plusquellic, D. and Jewell, P. (2005), Interstellar Isomers: The Importance of Bonding Energy Differences, Astrophysical Journal (Accessed June 19, 2024)


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Created October 9, 2005, Updated October 12, 2021