N2 Chemistry in Interstellar and Planetary Ices: Radiation-Driven Oxidation

As part of our work on nitrogen-rich ices, the IR spectra and band strengths used in a recent paper to identify and quantify radiation-induced changes in an N2+H2O ice near 15 K are examined, along with reports of (i) a chemical tracer for N2+H2O ices, (ii) a new IR feature of solid N2, and (iii) a striking 15N isotopic enrichment. Problems are found for each IR band strength used and for each of the three claims made, to the extent that none are supported by the results presented to date. In contrast, new work presented here, combined with several older investigations, strongly supports the formation of di- and triatomic nitrogen oxides in irradiated N2-rich ices. Observations and trends in the chemistry of N2-rich icy solids are described, and conclusions are drawn. A considerable amount of material from previous chemical studies of N2-rich systems, spanning more than a century, is brought together for the first time and used to examine the chemistry of N2-rich ices in extraterrestrial environments. Needs are identified and suggestions made for future studies of N2-rich interstellar and planetary ice analogs