Untangling the Formation of Methoxymethanol (CH 3 OCH 2 OH) and Dimethyl Peroxide (CH 3 OOCH 3 ) in Star-forming Regions

Abstract

Methoxymethanol (CH 3 OCH 2 OH) 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 (HOCH 2 CH 2 OH) and the hitherto unobserved dimethyl peroxide (CH 3 OOCH 3 ) are still elusive. Here, we report the very first confirmed synthesis of dimethyl peroxide—at various deuteration levels within interstellar analogous ices of D 3 -methanol (CD 3 OH) 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 (CH 3 O) and hydroxymethyl (CH 2 OH). 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.