Hydrogen abstraction in astrochemistry: formation of ˙CH₂CONH₂ in the reaction of H atom with acetamide (CH₃CONH₂) and photolysis of ˙CH₂CONH₂ to form ketene (CH₂CO) in solid para-hydrogen

Abstract

The amide bond of acetamide is unaffected by hydrogen exposure, but the hydrogen abstraction on its methyl site activates this molecule to react with other species to extend its size as a first step to form interstellar complex organic molecules.

Hydrogen Abstraction of Acetic Acid by Hydrogen Atom to Form Carboxymethyl Radical •CH2C(O)OH in Solid para-Hydrogen and Its Implication in Astrochemistry

“…The PES indicates that the reaction H + CH 3 C­(O)­OH → •CH 2 C­(O)­OH + H 2 has a relatively large barrier, 43 kJ mol –1 ; our experimental observation of •CH 2 C­(O)­OH at 3.3 K even in darkness indicates that this reaction occurred via tunneling. Similar H atom tunneling reactions have been observed for the reactions of H atoms with HONO (∼21 kJ mol –1 ), CH 3 OH (∼35 kJ mol –1 ), , H 2 NC­(O)H (∼26 kJ mol –1 ), C 5 H 5 N (∼8 kJ mol –1 ), HC­(O)­OCH 3 (∼41 and 46 kJ mol –1 for the formation of HC­(O)­CH 2 and C­(O)­OCH 3 radicals, respectively), and CH 3 CONH 2 (∼41 kJ mol –1 ); predicted barriers are provided in parentheses. Paulson et al photolyzed HC­(O)­OH in solid p -H 2 at 1.7 K with laser light at 193 nm and observed tunneling reaction H + HC­(O)­OH because some H atoms were produced from photolysis; the reaction proceeded even after photolysis was terminated, resulting in the formation of HOCO from abstraction of the hydrogen on the carbon atom rather than the hydroxyl hydrogen.…”

“…These experiments are not meant to mimic the conditions in interstellar ices but rather serve as a model system to study the tunneling reactions of H atoms. In our previous investigations on reactions of H atoms with methanol CH 3 OH, formamide HC­(O)­NH 2 , methyl formate HC­(O)­OCH 3 , and acetamide CH 3 C­(O)­NH 2 , we found that the previously neglected H-abstraction plays an important role. For example, in the reaction H + HC­(O)­NH 2 , the dual-cyclic hydrogen-abstraction and hydrogen-addition connecting HC­(O)­NH 2 , H 2 NCO, and HNCO can explain the tight relation between astronomical abundances of HC­(O)­NH 2 and HNCO …”

Preparation and characterization of the enol of acetamide: 1-aminoethenol, a high-energy prebiotic molecule

“…CH 4 -HNCO ice mixtures at 20 K were irradiated with vacuum ultraviolet (VUV) photons to produce the radicals required for the formation of the amides, which then were identied by IR spectroscopy as well as mass spectrometry. 41 Recently, Haupa et al 45 found that the reaction of atomic hydrogen with acetamide in solid p-H 2 at 3.3 K produces the 2-amino-oxoethyl (cCH 2 CONH 2 ) radical, which further dissociates to ketene and cNH 2 upon UV/vis photolysis.…”

Successive Hydrogenation of SO and SO2 in Solid para-H2: Formation of Elusive Small Oxoacids of Sulfur

“…In the first set of experiments, H atoms were generated by the method described in the studies of Anderson as well as Lee and co-workers. − For this, a second leak valve and stainless steel capillary were used to introduce Cl 2 to the main chamber. The SO 2 / para -H 2 ratio was 1:5500.…”

“…It is taking advantage of the phenomenon of quantum diffusion that allows for the efficient movement of the H atoms through the matrix, facilitating H addition and abstraction reactions. − Earlier studies in para -H 2 reported the successful hydrogenation of polycyclic aromatic hydrocarbons (PAHs), − HONO, isoprene, propene, and pyrrole . Hydrogen abstraction from the isolated molecule by the H atoms could also be detected recently in the case of formamide, methyl formate, and acetamide. − As it was shown by these studies, even if a H addition or a H abstraction reaction has a substantial barrier, it can be fast enough at very low temperatures due to H atom tunneling to observe it on the laboratory time scale. para -H 2 has a further important advantage; it is an excellent matrix material because it interacts weakly with the guest molecules.…”