Fig. 5.

Summary of the chemical routes proposed for the formation of EtA in the ISM. The molecular species in red have been detected toward the G+0.693 molecular cloud. The gray shaded area corresponds to a hydrogenation chain. The chemical reactions indicated with colored arrows have been proposed in previous work: magenta (36), blue (38), orange (41), cyan (39), and green (41, 47). In black, we show the formation routes proposed in this work. The solid arrows indicate surface chemistry reactions, and dashed arrows denote gas-phase chemistry.