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 (0,11d,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 exclusivley samples the "hot core", is 1.7×1016cm-2 and can be understood in terms of the "doughnut" model for Orion. Radiative excitation by 14 μm flux from IRc2 accounts for the (0,1,0) population, provided the hot core is ≡ 6 - 7×1016cm distant from IRc2. Toward IRC +10216 the authors have detected J = 3-2 transitions of both (0,11c,1d,0) and (0,20,0) excited states.