Synthesis of HCN and HNC in Ion-Irradiated N2-Rich Ices

by: Moore, M. H.; Hudson, R. L.; Ferrante, R. F.

ABSTRACT

Near-IR observations reveal that N2-rich ice containing small amounts of
CH4, and CO, is abundant on the surfaces of Triton, a moon of Neptune, and
Pluto. N2-rich ices may also exist, in interstellar environments. To
investigate the radiation chemistry of such ices we performed a systematic
IR study of ion-irradiated Nz-rich mixtures containing CH4 and CO. Irradia-
tion of N2 CH4 mixtures at 12 K, showed that HCN, HNC, diazomethane, and
NH3 were produced. We also found that UV photolysis of these ices produced
detectable HCN and HNC. Intrinsic band strengths, A(HCN) and A(HNC), were
measured and used to calculate yields of HCN and HNC. Similar results were
obtained on irradiation of N2 CH4 CO ices at 12 K, with the main difference
being the formation of HNCO. In all cases we observed changes on warming.
For example, when the temperature of irradiated Nz CH4 CO was raised from
12 to 30 K, HCN, HNC, and HNCO reacted with NH3, and OCN-, CN-, N3-, and
NH4 were produced. These ions, appearing at 30 K, are expected to form and
survive on the surfaces of Triton, Pluto, and interstellar grains. Our
results have astrobiological implications since some of these radiation
products are involved in the syntheses of biomolecules such as amino acids
and peptides.

CASI, Document ID 20030058927, 2001.