Detection of an absorption feature at the position of the 4 . 27 - m band of solid CO 2 ?

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 11.6 m. In addition to a number of well-known interstellar bands due to various molecular ices, a new band at 4.27 m 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.