Laboratory Detection of the Methoxymethyl Radical, CH₃OCH₂, Using Faraday Rotation and Chirped-pulse Techniques in the (Sub)millimeter Wave Range

Abstract Modeling the abundance of interstellar complex organic molecules in space is a major challenge for astrophysicists. The relative roles of gas-phase and grain-surface processes in the formation and destruction of such large molecules remain unclear. Methyl formate (CH 3 OCHO, MF) and dimethyl ether (CH 3 OCH 3 , DME) species have been detected at relatively high abundances in both warm and cold objects of the interstellar medium (ISM), challenging an initial hypothesis favoring grain-surface processes for their formation. In this context, the methoxymethyl radical (CH 3 OCH 2 , RDME) has been proposed as a key species linking the abundances of MF and DME in the gas phase. Its detection may provide crucial information to disentangle and quantify the different processes involved in the formation and destruction of MF and DME. To support the search for RDME in space, we present the laboratory detection of its pure rotational spectrum in the vibronic ground state. Special care was taken to measure the frequencies of transitions expected to be intense under cold interstellar conditions. In total, we assigned and fitted 1007 transitions of the RDME with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>′</mml:mo> </mml:mrow> </mml:msup> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>a</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>′</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> values up to 34 and 5, respectively. A reliable spectral catalog has been generated using the spectroscopic parameters derived from the fit and can be used confidently for future searches of the RDME radical in the ISM.