A chemical link between interstellar isopropanol and acetone: H atom reactions in solid para-hydrogen

Isopropanol [2-propanol, H3CCH(OH)CH3, IPA] and acetone [H3CC(=O)CH3] have been isolated in cryogenic para-H2 matrices at 3.1 K and were exposed to in situ generated H atoms. The reaction between the precursor molecules and H atoms was followed by Fourier-transform infrared (FT-IR) spectroscopy. The appearance of multiple new IR bands was attributed to products of H atom addition/abstraction processes. The experimental work was supported by quantum-chemical computations, helping in the IR spectroscopic assignments. The most important reaction product was the 2-hydroxy-2-propyl radical [CH3C•(OH)CH3] in both the acetone and IPA experiments. This radical may either form upon the abstraction of one H atom from the central C atom of the IPA molecule or when an H atom is directly added to the O atom of the acetone molecule. In addition, the formation of acetone and methane (CH4) from IPA was also observed, whereas the hydroxymethyl radical (•CH2OH) formed when acetone was exposed to H atoms. The results were further corroborated by secondary UV photolytic studies, which also resulted in the formation of photolytic products, such as methyl radical (•CH3), carbon monoxide (CO), and formaldehyde [HC(=O)H]. The main product, CH3C•(OH)CH3, was found to be sensitive to UV light and quickly decomposed to acetone. From an astrochemical perspective, the results demonstrate that there is a direct chemical relationship between acetone and IPA through H-atom reactions. Furthermore, if the radical formed in the reaction recombines with another radical in which the radical center is located on a carbon atom, a branched-carbon chain compound is produced.