DPS 2001 meeting, November 2001
Session 62. Laboratory Studies
Oral, Chairs: R. Wu, R. Hudson, Saturday, December 1, 2001, 4:40-5:50pm, Regency GH

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[62.04] IR Studies of Irradiated N2 Ices Containing CH4 and CO: Implications for Triton and Pluto

M. H. Moore (Nasa/Goddard Space Flight Center), R. L. Hudson (Eckerd College), R. F. Ferrante (US Naval Academy)

N2, CH4, and CO ices have been identified in the IR spectrum of Pluto. These same ices are present on Triton along with separated terrains of H2O and CO2. The focus of this presentation is the evolution of N2-rich ices containing CH4 and CO, where the evolution is driven by processing from energetic particles and possibly from vacuum-UV photons. Although surface temperatures near 35 K apply to Triton and Pluto, our 13 K studies probe the underlying chemical pathways, which lead to the formation and stability of expected surface products.

We have completed the first systematic IR study of ion-irradiated ices dominated by N2 and containing small amounts of CH4. HCN, HNC, and diazomethane, CH2N2, are formed after irradiation at 13 K. The identification of these products is consistent with extensive isotopic-substitution experiments. We have evidence that HCN and HNC form in irradiated N2 + CH4 ices (100:1), but not in binary mixtures containing N2 and C2H6, C2H4, C2H2, or methanol. Radical species identified after irradiation are N3, CH3, and C2H5. CN- and N3- were also detected. In comparison, photolyzed N2 + CH4 (100:1) forms CH2N2 and C2H2, but NOT detectable amounts of HCN, HNC, the N3 radical, or N3-. Irradiated N2 + CH4 + CO ices form HNCO in addition to the species found in irradiated N2 + CH4. These low-temperature studies allow us to identify radiation products rigidly trapped in the N2 matrix before they undergo reactions triggered by warming to 35 K. Implications of our low-temperature results for Triton and Pluto will be discussed along with possible formation mechanisms for HCN and HNC from CH4 diluted in N2 matrices

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