Nitrogen Sublimation as a Driver of Chemistry in Pluto-Analog Laboratory Ices: Formation of Carbon Suboxide (C3O2) and Various Salts

Abstract

A number of planetary bodies, including Triton and Pluto, and a number of Kuiper Belt objects contain nitrogen ices on their surfaces. Nitrogen ices were also used in laboratory experiments as a matrix isolation material before noble gases could be condensed. Planetary bodies with nitrogen ices then may act as giant matrix isolation experiments, trapping reactive species onto the surface and concentrating them. Upon sublimation, these reactive species are much more likely to encounter each other or another molecule to react with. A pilot study was conducted to test the feasibility of testing the chemistry occurring during the sublimation of nitrogen ices. A high vacuum laboratory setup was used to create ices at ∼6 K (±0.5 K). Ices were deposited under microwave radiation to create radicals to simulate what might be present in the tenuous atmospheres of these planetary bodies. The ices consisted of a mixture of 1:1:100 carbon source + H2O + N2, where the carbon source was either CO or CH4. Reagents and products were primarily identified using FTIR and UV–vis transmission spectroscopy. Once the predominantly N2 ice was characterized with the spectroscopic techniques, the N2 was sublimated to create a H2O ice, and then this ice was characterized using the aforementioned techniques. One completely new product was observed, namely, carbon suboxide (C3O2), and a couple products identified in the nitrogen ice formed various salts. Future work could make use of multiple sublimation steps and other astrochemically relevant matrices and introduce more astrophysically relevant sources of radiation like electron beams or UV irradiation.