Work

Formation of nitriles and isonitriles by the heavy-ion irradiation of propionitrile in N 2 -rich astrophysical ices

Year: 2026

Type: article

Abstract: Context. Nitriles are key nitrogen-bearing organic molecules in dense clouds, star-forming regions, and nitrogen-rich icy environments. Understanding their stability and chemical evolution under energetic processing is essential for understanding the formation of complex organic species in astrophysical ices. Aims. We investigate the radiolytic processing of propionitrile (CH 3 CH 2 CN, hereafter referred to as PCN) in a nitrogen-rich ice matrix and evaluate the formation of nitriles, isonitriles, hydrocarbons, and other nitrogen-bearing products induced by swift heavy ions. Methods. A PCN:N 2 ice mixture with an approximate molecular ratio of 1:10 was deposited at 10 K and irradiated with 40 MeV 40 Ar 9+ ions up to a fluence of 1 × 10 13 ions cm −2 . The chemical evolution was monitored in situ by Fourier-transform infrared spectroscopy. Destruction and formation cross sections, as well as radiation chemical yields, were derived from the fluence dependence of selected infrared bands. Results. Ion irradiation efficiently destroys PCN and produces a rich inventory of daughter species. The products include: nitriles and isonitriles such as HCN, HCNN, HC 3 N, CH 3 CN, CH 3 C 3 N, CH 3 CHCNH, CH 2 CHCN, NCCN/C 2 N 2 , CN, and C 2 N; nitrogen-bearing species such as CH 2 NH, CH 3 NH 2 , CH 3 N 3 , and N 3 - ; and hydrocarbons, including CH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 , and C 4 H 4 . The derived cross sections indicate that CN-bearing fragments and hydrocarbons are among the most efficiently formed products, demonstrating that the C≡N group is efficiently preserved and that extensive carbon-chain reorganization also occurs. Conclusions. The results demonstrate that the energetic processing of PCN in N 2 -rich ices provides an efficient pathway to molecular complexity under conditions relevant to dense interstellar clouds, protostellar environments, and nitrogen-rich outer Solar System surfaces.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202661859