2002A&A...390.1075G

We report on a search for the NH₃ inversion band at 9.0µm, the CH₄ band at 7.7µm, and the CH₃OH band at 9.7µm in the spectra of 10 heavily obscured stellar objects taken with the spectrophotometer ISOPHOT-S aboard the Infrared Space Observatory (ISO). Four of them show indications of the NH₃ inversion band at 9.0µm superimposed on the always strong silicate band. The results show that ammonia ice may be abundant in some cool and dense molecular circumstellar regions. The 9.7µm band of solid CH₃OH was detected in 5 of the sources, and also the 7.7µm band of solid CH₄ was found in 5 sources. The PHT-S detections were cross-checked against ISO-SWS spectra from archive data. Considering the different beam sizes (24x24"² versus 14x20"²), there is good agreement.