2018ApJ...859...59B

We report the first confirmed synthesis of ethyl methyl ether (EME, CH₃CH₂OCH₃) within astrophysical model ices containing water (H₂O) and methane (CH₄) exposed to ionizing radiation at ultra-low temperatures of 5 K. EME (also known as methoxyethane), was recently observed toward Orion KL and currently is the largest confirmed oxygen-bearing molecule found in the interstellar medium. Exploiting isomer-selective photoionization (PI) of the subliming molecules in the temperature-programmed desorption phase at 10.49, 9.92, and 9.70 eV, coupled with reflectron time-of-flight mass spectrometry and isotopic substitution experiments (H₂¹⁸O-CH₄), the detection of fragment ions of EME at m/z = 45 (C₂H₅O⁺) and m/z = 59 (C₃H₇O⁺), and probing the proton transfer in subliming ethanol-EME complexes via m/z = 61 (C₃H₉O⁺), the present study reveals that EME can be formed from suprathermal reactions initiated by cosmic rays and secondary electrons generated within astrophysical ices. The detection of EME in our experiments represents a significant advance in the understanding of formation pathways of complex organic molecules present in hot cores and helps to constrain astrochemical models on the formation of such species within molecular clouds.