Radiation-induced degradation of acetic acid molecules in cryogenic media: diverse chemistry revealed by a matrix isolation FTIR study

Abstract

Acetic acid is one of the key simple organic molecules in various processes ranging from industrial applications to atmospheric and interstellar chemistry. In particular, it may be important in the radiation-induced processing of astrophysically relevant ices leading to prebiotic molecules. Here we report a detailed systematic study on the mechanisms of degradation of acetic acid molecules isolated in rigid inert cryogenic media under the action of X-rays and vacuum ultraviolet (VUV) radiation using Fourier transform infrared (FTIR) spectroscopy. The obtained results revealed the products originating from dehydrogenation (trans-˙CH₂COOH), C–O bond cleavage (H₂CCO⋯H₂O and H˙CCO⋯H₂O), C–C bond cleavage (CH₄, CO₂, and ˙CH₃⋯CO₂), and simultaneous (or consecutive) cleavage of both C–O and C–C bonds (CH₃OH⋯CO, H₂CO, H˙CO, and CO). It was found that the C–O bond cleavage occurs more efficiently in low-polarizable light-atom matrices (Ne and Ar), whereas the C–C bond rupture and (presumably) dehydrogenation channels are more favorable in Xe. Comparison between X-ray radiolysis and VUV-photolysis suggests that the ionic process may play an important role in the C–C bond rupture and possibly in dehydrogenation. It should be noted that the radiation-induced transformations of isolated acetic acid molecules reveal remarkable diversity of the reaction channels, essentially different from those observed for the radiolysis of neat acetic acid in condensed phases.