title: Cyanide and isocyanide abundances in the cold, dark cloud TMC-1.
abstract: We have observed emission from HCN, H13CN, HC15N, HN13C, H15NC, HC3N, CH3CN, and possibly CH3NC, and determined an upper limit for NH2CN, toward the cold, dark cloud TMC-1.  The abundance ratio [HNC]/[HCN] = 1.55 +/- 0.16 is at least a factor approximately 4 and approximately 100 greater than that observed toward the giant molecular clouds DR 21(OH) and Orion KL, respectively.  In contrast, for the corresponding methylated isomers we obtain [CH3NC]/CH3CN] < or approximately 0.1.  We also find [NH2CN]/[CH3CN] < or approximately 0.1 and [HC3N]/[CH3CN] = 30 +/- 10.  We find no evidence for anomalous hyperfine ratios for H13CN, indicating that the ratios for HCN (cf. recent work of Walmsley et al.) are the result of self-absorption by cold foreground gas.
authors.affiliation: Department of Physics and Astronomy, University of Massachusetts, USA.
authors.forename: W M
authors.initials: WM
authors.lastname: Irvine
authors.forename: F P
authors.initials: FP
authors.lastname: Schloerb
mesh_terms: D055580:Astronomical Phenomena; D001256:Astronomy; D003486:Cyanides / Q000032:analysis*; D005118:Extraterrestrial Environment; D005740:Gases / Q000032:analysis*; D006856:Hydrogen Cyanide / Q000032:analysis*; D007536:Isomerism; D009570:Nitriles / Q000032:analysis
chemical_list: D003486:Cyanides; D005740:Gases; D009570:Nitriles; D006856:Hydrogen Cyanide