2019ApJ...881..156Z

Methoxymethanol (CH₃OCH₂OH) was recently detected toward the MM1 core in the high-mass star-forming region NGC 6334I. However, the underlying formation mechanisms of this complex organic molecule (COM) as well as its structural isomers ethylene glycol (HOCH₂CH₂OH) and the hitherto unobserved dimethyl peroxide (CH₃OOCH₃) are still elusive. Here, we report the very first confirmed synthesis of dimethyl peroxide-at various deuteration levels within interstellar analogous ices of D₃-methanol (CD₃OH) exposed to ionizing radiation at ultralow temperatures of 5 K. The discrimination of specific isomers is achieved by exploiting reflectron time-of-flight mass spectrometry coupled with isomer-selective photoionization of the subliming molecules in the temperature programmed desorption phase of the experiment. Based on the distribution of the identified species at distinct mass-to-charge ratios, we reveal primary and secondary reaction pathways to methoxymethanol, ethylene glycol, and dimethyl peroxide involving radical-radical recombination of methoxy (CH₃O) and hydroxymethyl (CH₂OH). Our findings help to constrain the formation mechanism of COMs detected within star-forming regions (methoxymethanol, ethylene glycol) and propose that the hitherto elusive dimethyl peroxide isomer represents an excellent candidate for future astronomical searches.