Swift Heavy Ion-Induced Chemistry of CH3CN Ices at 10 and 80 K

Acetonitrile (CH3CN) is a key nitrogen-bearing molecule detected in a variety of astrophysical environments and is considered a potential precursor of prebiotic compounds. The study aimed to investigate the stability and radiation chemistry of 56Fe10+ ions at the Grand Accelerateur National d'Ions Lourds (GANIL). In situ FTIR spectroscopy revealed efficient molecular destruction accompanied by the formation of several nitrogen-bearing species, including HCN, H2C=C=NH, CH2CHNC, CH3CH=NH, H2C=NH, NCCN, and NH3 with possible contributions from the C-H such as CH4 and C-H stretching of HC3N and, to a lesser extent, the N-H stretch of ketenimine (H2C=C=NH). The apparent destruction cross section of CH3CN was found to be (2.3 +/- 0.8) & times; 10-12 cm2 at 10 K and (5.6 +/- 1.0)& times;10-12 cm2 at 80 K, indicating more extensive radiolytic processing at higher temperatures. Enhanced radical mobility at 80 K promotes hydrogenation and polymerization, leading to a refractory C-N-rich residue, whereas at 10 K intramolecular isomerization dominates. These results demonstrate that swift heavy-ion irradiation of nitrile ices efficiently produces small nitriles, isonitriles, and polyimines of astrochemical interest, supporting the role of CH3CN as a hidden precursor to prebiotic organic matter in interstellar and planetary ices.