Laboratory simulation of Kuiper belt object volatile ices under ionizing radiation: CO–N2 ices as a case study

Abstract

The exposure of icy Kuiper belt objects (KBOs) by ionizing radiation was simulated in this case of exposing carbon monoxide–nitrogen (CO–N₂) ices by energetic electrons. The radiation-induced chemical processing was monitored on-line and in situ viaFTIR spectroscopy and quadrupole mass spectrometry. Besides the array of carbon oxides being reproduced as in neat irradiated carbon monoxide (CO) ices studied previously, the radiation exposure at 10 K resulted in the formation of nitrogen-bearing species of isocyanato radical (OCN), linear (l-NCN), nitric oxide (NO), nitrogen dioxide (NO₂), plus diazirinone (N₂CO). The infrared assignments of these species were further confirmed by isotopic shifts. The temporal evolution of individual species was found to fit in first-order reaction schemes, prepping up the underlying non-equilibrium chemistry on the formation of OCN, l-NCN, and NO radicals in particular. Also unique to the binary KBO model ices and viable for the future remote detection is diazirinone (N₂CO) at 1860 cm⁻¹ (2ν₅) formed at lower radiation exposure.