1996A&A...315L.333S

Short Wavelength Spectrometer observations of the 6.0 and 6.8µm absorption features towards the obscured young stellar object NGC 7538: IRS9 are presented and compared to the features of a number of species measured in the solid phase. It is found that while solid H₂O provides the bulk of the 6µm band, additional absorption is required near 5.83µm and 6.25µm. It is proposed that formic acid (HCOOH) is a plausible candidate for the blue excess, while the red excess could be related to the C-C stretching mode in aromatic structures. Subsequently, a number of candidates for the 6.8µm band are reviewed. Unfortunately, none of these appears to satisfy the observational constraints and no plausible identification can at this point be presented.