DETECTION OF AN ABSORPTION FEATURE AT THE POSITION OF THE 4.27-MU-M BAND OF SOLID CO2

We report observations of 13 young infrared sources associated with mo lecular clouds with ISO's spectrophotometer ISOPHOT-S in the wavelengt h range from 2.5 to 11.6 mu m. In addition to a number of well-known i nterstellar bands due to various molecular ices, a new band at 4.27 mu m was detected, which is very likely attributed to C=O stretching vib rations 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 compar able amounts in the mantles. The implications for the models of inters tellar chemistry are briefly discussed.