Near-Infrared Vibrational Frequencies of HCN, HNC, and CN in N₂ and Ar Ice Matrices

The surfaces of cold objects in the outer Solar System, like those of Kuiper Belt objects, are often dominated by volatile ices such as nitrogen, methane, and carbon monoxide. As these icy surfaces are subjected to a variety of energetic particles and ultraviolet radiation, HCN and its irradiation products may form and thus contribute to the vibrational bands observed by telescopic and in situ near-infrared observations. Here, we provide frequency assignments for most near-infrared vibrational features (8000–4000 cm^–1, 1.25–2.5 μm) of HCN, HNC, the CN radical, and their ¹³C isotopologues in N₂ and Ar ice matrices. These were derived from transmission spectra of solid isolated HCN subjected to UV photolysis at 14 K. These frequencies can be used to search for HCN and its irradiation products in archival or in future observational data sets and thus further our understanding of the composition and the energetic processing of icy surfaces in the outer solar system.