Laboratory studies of the production of glycine from smaller precursors that mimic interstellar conditions have been extensive. Ultraviolet photolysis and electron bombardment of various interstellar ice analogs such as CO/NH3/H2O or H2O/CH3NH2/CO2 at low temperatures have been shown to yield glycine11,12,13,14,15,16,17,18. Recently, Ioppolo et al.19 observed that methyl amine glycine formed from ice containing CH3NH2, CO, O2, and atomic H under conditions similar to dark interstellar clouds; , that is, at an earlier stage of star formation than previously assumed. These authors propose that glycine is generated by a barrier-free radical-radical surface reaction (1), where • CH2NH2 is generated by abstraction of H from CH3NH2 by • OH (generated from H + O2) or H atoms, and • HOCO is • Between OH and CO produced by the reaction.

Although the free radical •CH2NH2 plays a key role in the formation of glycine, its spectrum and formation mechanism have not been directly determined. Bosa et al. The separation of this radical was reported to be difficult due to the recombination of CH3NH2 after recombination of CH2NH2 with H atoms; thus, they used CO as a hydrogen atom scavenger to reduce the recombination, but in VUV of CH3NH2/CO binary ice mixture ( Vacuum ultraviolet light) irradiation, only formamide and N-methylformamide were observed instead of CH2NH220.

Here we provide direct experimental evidence by infrared spectroscopy that at low temperatures, even in the dark, H atoms react with CH3NH2 via H-extraction tunneling to form CH2NH2 and CH2NH. In addition, our experimental results reveal a tight chemical link between CH3NH2 and CH2NH through dihydroextraction and hydrogenaddition cycles.

Results and discussion
To perform the H atom reaction in the laboratory, we co-deposited Cl2, CH3NH2, and parahydrogen (p-H2) at 3.2 K, and illuminated the substrate with 365 nm light from a light-emitting diode followed by infrared irradiation. Cl2 at 365 nm UV photolysis produces Cl atoms, which are stable towards H2 because the reaction Cl + H2 〈 〈HCl + 〉H is endothermic and has a large potential barrier21. Subsequent infrared radiation excites H2 from ν = 0 to ν = ⟩1 to overcome the energy limitation, allowing Cl atoms to react with H2 (ν = ⟩1) to form HCl + ⟩H. The resulting H atoms react with CH3NH2 during infrared radiation, but even if the matrix is kept in the dark for a long time, the reaction continues because the H atoms can migrate slowly in the matrix by tunneling reactions to break and form adjacent H The −H bond (so-called quantum diffusion) approaches CH3NH2 and reacts via tunneling. Efficient production of Cl by photolysis of Cl2 in low-temperature substrates requires reduced cage effects, H2 (ν = ⟩1) is required for H production, and quantum tunneling reactions are required for H migration in the dark; all of these are only possible in quantum Only possible in solid p-H2