On the correlation of the abundances of HNCO and NH₂CHO: Advantages of solid para-H₂ to study astrochemical H-atom addition and abstraction reactions

Abstract

In dense interstellar clouds that are shielded from high-energy radiation (e.g., UV photons or cosmic rays), H-atom addition and abstraction reactions that take place on grain surfaces play principal roles in the synthesis or decomposition of complex organic molecules (COMs). These reactions are extensively investigated with laboratory experiments by bombarding astrophysical analogue ices with a beam of low-temperature H atoms. Here we demonstrate that, although 2-4 K solid para-H2 does not represent a typical environment of the surface of interstellar grains, para-H2 matrix isolation combined with IR spectroscopy is a complementary tool to sensitively detect astrochemical hydrogenation and dehydrogenation processes.

Non-energetic, Low-Temperature Formation of Cα-Glycyl Radical, a Potential Interstellar Precursor of Natural Amino Acids

“…32,39 This is based on the works of Anderson as well as Lee and coworkers. 24 Cl 2 in the matrix was first decomposed by laser irradiation at 365 nm (Cl 2 → 2Cl • ), followed by 2217 nm laser light to generate H atoms (H 2 + Cl → HCl + H). Figures 2e and 3b show the difference spectra obtained by subtracting the IR spectrum recorded after the 365 nm irradiation from the IR spectrum taken after the generation of H atoms by NIR irradiation and waiting 9 h in the dark.…”

“…The weakly interacting medium provides ideal conditions for sensitive spectroscopic detection of the reaction products. The advantages and limitations of this method for astrochemical studies have been discussed, and the technique was recently applied to study several H-atom-abstraction and H-atom-addition reactions. ,− …”

“…Generally, H atoms can react with an H-containing molecule in solid para -H 2 in either an H-abstraction or an H-addition reaction. Despite that a radical is formed from a closed-shell molecule, both types of reactions are usually favored thermodynamically due to the high-energy reactant H atom. − …”

“…To create H atoms for reaction with glycine, the same method was used as described previously in detail. , This is based on the works of Anderson as well as Lee and co-workers . Cl 2 in the matrix was first decomposed by laser irradiation at 365 nm (Cl 2 → 2Cl • ), followed by 2217 nm laser light to generate H atoms (H 2 + Cl → HCl + H).…”

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

“…This method, with its advantages and certain limitations, should be considered to be complementary to typical astrophysical experiments of ice analogues. 149 On the other hand, the hydrogenation of SO 2 by direct UV photolysis is anticipated to appropriately mimic the environment on Jovian satellites that have solid SO 2 on their surfaces, leading to the formation of SO, and furthermore, with superficial H 2 O ice that may serve as a H atom source upon energetic irradiation. 150,151 These observations presented here shed light on these, previously mostly unknown, processes and eventually help us understand and therefore predict the (astro)chemistry of SOS in the ISM and on the surface of celestial bodies better.…”