title: Detection of interstellar vibrationally excited HCN.
abstract: Vibrationally excited HCN has been observed for the first time in the interstellar medium.  The J = 3-2 rotational transitions of the l-doubled (0,1(1d,1c), 0) bending mode of HCN have been detected toward Orion-KL and IRC +10216.  In Orion, the overall column density in the (0,1,0) mode, which exclusively samples the "hot core", is 1.7 x 10(16) cm-2 and can be understood in terms of the "doughnut" model for Orion.  The ground-state HCN column density implied by the excited-state observations is 2.3 x 10(18) cm-2 in the hot core, at least one order of magnitude greater than the column densities derived for HCN in its spike and plateau/doughnut components.  Radiative excitation by 14 micrometers flux from IRc2 accounts for the (0,1,0) population, provided the hot core is approximately 6-7 x 10(16) cm distant from IRc2, in agreement with the "cavity" model for KL.  Toward IRC +10216 we have detected J = 3-2 transitions of both (0,1(1c),(1d), 0) and (0, 2(0), 0) excited states.  The spectral profiles have been modeled to yield abundances and excitation conditions throughout the expanding envelope.
authors.affiliation: Five College Radio Astronomy Observatory, University of Massachusetts, Amherst, USA.
authors.forename: L M
authors.initials: LM
authors.lastname: Ziurys
authors.forename: B E
authors.initials: BE
authors.lastname: Turner
mesh_terms: D055580:Astronomical Phenomena; D001256:Astronomy; D003198:Computer Simulation; D005118:Extraterrestrial Environment; D006856:Hydrogen Cyanide / Q000032:analysis*; D008872:Microwaves; D008962:Models, Theoretical; D013057:Spectrum Analysis
chemical_list: D006856:Hydrogen Cyanide