Carbon suboxide in astrophysical ice analogs

As suggested by W. T. Huntress et al. (1991, Nature 352, 316318), carbon suboxide (C3O2) is a potential extended source of both the CO and atomic carbon emission observed in cometary comae. However, laboratory experiments on the formation and stability of C3O2 in space environments have not been published. In this work, we study solid C3O2 in ices representative of cometary nuclei as well as interstellar icy grain mantles, specifically addressing the issues Of C3O2 formation and stability under exposure to energetic processing in the forms of proton irradiation and UV photolysis. The formation rate Of C3O2 is measured in laboratory ices of pure CO and CO2 and mixtures of these molecules with H2O at 18 K. Destruction rates in H2O-dominated mixtures appropriate to a cometary nucleus or interstellar icy grain mantle are also measured. Differences in rates between photolysis and irradiation experiments are observed and quantified. Mid-infrared spectra Of C3O2-containing mixtures are presented together with measurements of carbon suboxide's infrared band strengths and vapor pressures from 110 to 125 K. Implications are discussed for the existence Of C3O2 under the energetic conditions found in astrophysical environments as well as the possibility for its detection in cometary and/or interstellar ices. (C) 2001 Elsevier Science (USA).