There is an increasing evidence for the existence of large organic moleculesin the interstellar and circumstellar medium. Very few among such species arereadily formed in conventional gas-phase chemistry under typical conditions ofinterstellar clouds. Attention has therefore focused on interstellar ices as a potentialsource of these relatively complex species. Laboratory experiments showthat irradiation of interstellar ice analogues by fast particles or ultraviolet radiationcan induce significant chemical complexity. However, stars are sources ofintense X-rays at almost every stage of their formation and evolution. Such radiationmay thus provide chemical changes in regions where ultraviolet radiationis severely inhibited.After H2O, CO is often the most abundant component of icy grain mantles indense interstellar clouds and circumstellar disks. In this work we present irradiationof a pure carbon monoxide ice using a soft X-ray spectrum peaked at 0.3 keV.Analysis of irradiated samples shows formation of CO2, C2O, C3O2, C3, C4O andCO3/C5. Comparison of X-rays and ultraviolet irradiation experiments, of thesame energy dose, show that X-rays are more efficient than ultraviolet radiationin producing new species. With the exception of CO2, X-ray photolysis inducesformation of a larger number of products with higher abundances, e.g., C3O2column density is about one order of magnitude higher in the X-ray experiment.To our knowledge this is the first report on X-ray photolysis of CO ices. Thepresent results show that X-ray irradiation represents an efficient photo-chemicalway to convert simple ices to more complex species.
|Numero di pagine||5|
|Rivista||THE ASTROPHYSICAL JOURNAL LETTERS|
|Stato di pubblicazione||Published - 2012|
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science
Barbera, M., Jiménez-Escobar, Muñoz Caro, Giarrusso, Collura, Cecchi-Pestellini, Ciaravella, & Candia (2012). SOFT X-RAY IRRADIATION OF PURE CARBON MONOXIDE INTERSTELLAR ICE ANALOGUES. THE ASTROPHYSICAL JOURNAL LETTERS, 746, L1-L5.