A New Unidentified Far‐Infrared Band in NGC 7027

We report on the detection of a molecular band centered at ~98 μm (~102 cm -1 ), 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 ν 9 and ν 7 bending modes of C 6 and C 5 , for which wavenumbers of 90 ± 50 and 107 ± 5 cm -1 have been estimated from photoelectron spectroscopy.