2004A&A...425..767Y

The rotational spectrum of the semistable HC₅N molecule has been investigated in the millimeter-wave region for eight excited bending states which lie below 500cm^–1, namely v₁₁=1,2,3, and 4, v₁₀=1, v₉=1, (v₁₀=1, v₁₁=1), and (v₁₀=1, v₁₁=2). Transitions up to J=101←100 were measured, reaching a frequency as high as 270 GHz. The set of spectroscopic constants determined in the present work makes it possible to predict with much improved accuracy the transition frequencies of millimeter-wave lines produced by vibrationally excited HC₅N in hot core molecular sources and circumstellar shells. In addition, results of extensive CCSD(T) calculations are presented, which yield accurate term values for low-lying bending vibrational states.