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

Rosemonde Chahbazian, Marie-Aline Martin-Drumel, Olivier Pirali
The Astrophysical Journal
982,
162
(2025)
Open access
© The Author(s) 2025 · CC BY 4.0
First page of Chahbazian et al. 2025, The Astrophysical Journal
Chahbazian et al. (2025)
The Astrophysical Journal 982, 162
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Research overview

Researchers at the Institut des Sciences Moléculaires d’Orsay recorded the first laboratory rotational spectrum of the methoxymethyl radical (CH₃OCH₂). This radical is thought to link methyl formate and dimethyl ether in interstellar gas-phase chemistry. They made it by fluorine-atom H-abstraction from dimethyl ether and measured it from 140 to 650 GHz, using Faraday-rotation spectroscopy alongside chirped-pulse techniques. Faraday rotation detects only magnetic (paramagnetic) species, which filters out most lines from the precursor. In total, 1007 transitions were assigned and fitted. The result is a reliable catalogue for radio-astronomical searches. Two wire-grid polarizers set the polarization at the cell entrance and analyse it at the cell output.

Key findings

  • The first laboratory detection of the rotational spectrum of the methoxymethyl radical (CH₃OCH₂), a proposed link between methyl formate and dimethyl ether in the interstellar medium.
  • 1007 transitions were assigned and fitted, with N up to 34 and Ka up to 5, giving a reliable catalogue for searches in space.
  • Faraday-rotation spectroscopy from 140 to 650 GHz filtered out most lines from the dimethyl ether precursor and separated the spin–rotation components by their phase.
  • A polarizing grid at the cell entrance cleaned the input polarization, and a second grid at 45° at the output turned the polarization rotation into a measurable amplitude signal.
Purewavepolarizer 10 micron wire grid polarizer image

10 µm Free-Standing THz Wire-Grid Polarizer

PW010-040 (10 µm tungsten wires, 40 µm period, 0.1–1.1 THz) and PW010-025 (10 µm wires, 25 µm period, 0.1–4 THz). Used as the input polarizer and the 45° analyser grid in Faraday-rotation spectroscopy from 140 to 650 GHz.
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“The (sub)mmW emitted radiation is a well-defined vertical linear polarization that we further polarize by placing a polarization grid at the entrance of the cell. To convert the polarization modulation into amplitude modulation, we placed a polarization grid rotated by an angle θ = 45° at the output of the cell.”
Chahbazian et al.,
2025

Publication details

Journal

The Astrophysical Journal

Volume

982

Issue

Article

162

Published

2025

Research area

Spectroscopy and Molecular Physics

Application

Faraday-rotation rotational spectroscopy of an interstellar radical

Licence

© The Author(s) 2025 · CC BY 4.0

Institution

Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d’Orsay

DOI

https://doi.org/10.3847/1538-4357/adba5c

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