2025ApJS..277...14Z

Ethanolamine (NH₂CH₂CH₂OH) can form not only glycine directly under the conditions of proposed Archean alkaline hydrothermal vents, a possible environment for the origin of life, but also the polar hydrophilic head of phosphatidylethanolamine, the second most abundant phospholipid in cell membranes, under possible conditions of the primitive Earth. Recently, NH₂CH₂CH₂OH was detected toward the G+0.693-0.027 molecular cloud. We construct the chemical network for NH₂CH₂CH₂OH and its related species (HOCH₂CN, CH₃NH₂, NH₂OH, CH₃OH, C₂H₅OH, and C₂H₃OH) via quantum chemical calculations, simulate their abundance evolutions with the pnautilus code, and then acquire the best-fitting shock-wave model for G+0.693: the combination of isothermal model I₅ (T_g = T_d = 16 K, n_H = 4 × 10³ cm^–3, A_V = 6 mag, and ζ = 1.3 × 10^–15 s^–1) and continuous shock model S₅ (V_s = 20 km s^–1). We find NH₂CH₂CH₂OH mainly comes from the thermal desorption produced by shock-induced heating and the photodesorption generated by cosmic-ray-induced UV photons; overall, its ice-phase species is mostly produced by four sequential ice-phase addition pathways, in which the final reactions are J-H + J-NH₂CH₂CHOH → J-NH₂CH₂CH₂OH, J-H + J-NHCH₂CH₂OH → J-NH₂CH₂CH₂OH, J-H + J-NH₂CH₂CH₂O → J-NH₂CH₂CH₂OH, and J-CH₂OH + J-CH₂NH₂ → J-NH₂CH₂CH₂OH. We also discuss the formation of HOCH₂CN, CH₃OH, C₂H₅OH, and C₂H₃OH in the best-fitting shock-wave model, as well as the formation of NH₂CH₂CH₂OH in a typical hot-core model. Moreover, we predict NH₂CH₂CH₂OH may be detected toward the newly formed hot core; the undiscovered species CH₂CH₂OH and HOCCNH are potentially detectable toward G+0.693.