Radiolysis of H sub(2)O:CO sub(2) ices by heavy energetic cosmic ray analogs

An experimental study of the interaction of heavy, highly charged, and energetic ions (52 MeV super(58)Ni super(13+)) with pure H sub(2)O, pure CO sub(2) and mixed H sub(2)O:CO sub(2) astrophysical ice analogs is presented. This analysis aims to simulate the chemical and the physicochemical interactions induced by heavy cosmic rays inside dense and cold astrophysical environments, such as molecular clouds or protostellar clouds. The measurements were performed at the heavy ion accelerator GANIL (Grand Accé lé rateur National d’ Ions Lourds in Caen, France). The gas samples were deposited onto a CsI substrate at 13 K. In-situ analysis was performed by a Fourier transform infrared (FTIR) spectrometer at different fluences. Radiolysis yields of the produced species were quantified. The dissociation cross sections of pure H sub(2)O and CO sub(2) ices are 1.1 and 1.9 × 10 super(-13) cm super(2), respectively. For mixed H sub(2)O:CO sub(2) (10:1), the dissociation cross sections of both species are about 1 × 10 super(-13) cm super(2). The measured sputtering yield of pure CO sub(2) ice is 2.2 × 10 super(4) molec ion super(-1). After a fluence of 2& minus; 3 × 10 super(12) ions cm super(-2), the CO sub(2)/CO ratio becomes roughly constant (~0.1), independent of the initial CO sub(2)/H sub(2)O ratio. A similar behavior is observed for the H sub(2)O sub(2)/H sub(2)O ratio, which stabilizes at 0.01, independent of the initial H sub(2)O column density or relative abundance.