A new Unidentified Far Infrared Band in NGC 7027

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 can not be reproduced by atomic fine structure lines, recombination lines or by 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 ν9 and ν7 bending modes of C6 and C5, for which wavenumbers of 90±50 and 107±5 cm have been estimated from photoelectron spectroscopy. Subject headings: infrared: stars — circumstellar matter — stars: individual (NGC 7027) — ISM: molecules — line: identification