A chemical link between methylamine and methylene imine and implications for interstellar glycine formation

Methylamine CH₃NH₂ is considered to be an important precursor of interstellar amino acid because hydrogen abstraction might lead to the aminomethyl radical •CH₂NH₂ that can react with •HOCO to form glycine, but direct evidence of the formation and spectral identification of •CH₂NH₂ remains unreported. We performed the reaction H + CH₃NH₂ in solid p-H₂ at 3.2 K and observed IR spectra of •CH₂NH₂ and CH₂NH upon irradiation and when the matrix was maintained in darkness. Previously unidentified IR spectrum of •CH₂NH₂ clearly indicates that •CH₂NH₂ can be formed from the reaction H + CH₃NH₂ in dark interstellar clouds. The observed dual-cycle mechanism containing two consecutive H-abstraction and two H-addition steps chemically connects CH₃NH₂ and CH₂NH in interstellar media and explains their quasi-equilibrium. Experiments on CD₃NH₂ produced CD₂HNH₂, in addition to •CD₂NH₂ and CD₂NH, confirming the occurrence of H addition to •CD₂NH₂.