Processing of low carbon content interstellar ice analogues by cosmic rays: implications for the chemistry around oxygen-rich stars

• Published in: Monthly notices of the Royal Astronomical Society 2014-03, Vol.438 (3), p.2026-2035
• Main Authors: de Barros, A. L. F., da Silveira, E. F., Pilling, S., Domaracka, A., Rothard, H., Boduch, P.
• Format: Article
• Language: English
• Subjects: Astrophysics; Cosmic rays; Molecular physics; Physics; Sciences of the Universe; Spectrum analysis
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stt2305

Radiolysis of a homogeneous H2O:H2CO:CH3OH (100:2:0.8) ice mixture by fast heavy ions is performed in the laboratory in an attempt to simulate the interaction of cosmic rays with frozen surfaces at 15 K. Bombarded by 220-MeV 16O7 + ions, the ice layer is thin enough to be traversed by projectiles at approximately constant velocity and with charge states close to the equilibrium one. Analysis by Fourier transform infrared spectroscopy (FTIR) reveals that the molecular species formed are CH4, CO2, CO, HCO, HCOO− and CH3OCHO. The formation and dissociation cross-sections of all observed daughter molecules are determined. As a control procedure, a carbon budget is performed as the beam fluence increases. The observed radiation effects lead to a general observation that the destruction cross-sections of condensed gases by heavy ions are ruled by a power law that is a function of the electronic stopping power: σd ∼ , where n is approximately 3/2. This relation is observed for the destruction of precursor H2CO molecules and for the formation of daughter species. The present results help our understanding of the chemical and physicochemical interactions induced by heavy cosmic rays in cold astrophysical environments with low carbon contents, such as those around oxygen-rich stars.