1996A&A...315L.189G

We report observations of 13 young infrared sources associated with molecular clouds with ISO's spectrophotometer ISOPHOT-S in the wavelength range from 2.5 to 11.6µm. In addition to a number of well-known interstellar bands due to various molecular ices, a new band at 4.27µm was detected, which is very likely attributed to C=O stretching vibrations of solid CO₂. This new band is seen in all our sources. Thus, CO₂ seems to be a common constituent of icy grain mantles in molecular clouds. The strength of the band increases with the strengths of the CO and H₂O bands. We estimate that CO₂ and CO may be present in comparable amounts in the mantles. The implications for the models of interstellar chemistry are briefly discussed.