2004ApJ...609..225G

We report on the detection of a molecular band centered at ∼98 µm (∼102/cm), observed with the Infrared Space Observatory in the young planetary nebula NGC 7027. The band structure and intensity cannot be reproduced by atomic fine-structure lines, recombination lines, or the rotational emission of abundant molecules. We discuss the possible contribution of the low-energy bending modes of pure carbon chains to the unidentified far-IR bands observed in C-rich evolved objects. In particular, we speculate that the band emission could arise from the ν₉and ν₇bending modes of C₆and C₅, for which wavenumbers of 90±50 and 107±5/cm have been estimated from photoelectron spectroscopy.