The Interstellar Frozen CO Infrared Absorption Band in Nonpolar Ices
The infrared spectrum of the frozen CO feature in astrophysically relevant nonpolar ices was studied in an attempt to match the narrow interstellar feature at 2140 em-I. The best fits were obtained from laboratory ices which contained CO, N2, and a third component in comparable concentrations. Ices in which the third component was H20 or 02 provided good fits, while C02 did not prove to be a suitable third component. These ices matched the interstellar feature both bdore and after photolysis and at all temperatures between 12 and 30 K. The infrared-inactivity of N2 was broken in these ices, and a feature corresponding to the N2 stretch was observed at 2328 em-I. A second feature appears at 2348 cm-I in some cases. The origin of this band is puzzling. It does not appear to be due to C02 contamination, but is dependent on the presence of H20. Photolysis of the ices resulted in new photoproducts including C02, N20, 03, C03, HCO, and H2CO, which can be searched for in interstellar spectra. The triple bond of N2 was never broken in these experiments, and no singlynitrogenated products were formed.