Submillimeter-wave spectroscopy of the CH$_3$O radical

TL;DR

This study extends the submillimeter-wave rotational spectrum measurements of the CH$_3$O radical, improving spectroscopic parameters and enabling more accurate future detection in laboratory and interstellar environments.

Contribution

The paper provides new high-frequency spectral data and an improved effective Hamiltonian model for CH$_3$O, enhancing spectral predictions over a broad frequency range.

Findings

Extended the spectral measurements up to 860 GHz.

Achieved more accurate spectroscopic parameters.

Enabled reliable spectrum calculations for future searches.

Abstract

The methoxy radical, CH$_3$O, has long been studied experimentally and theoretically by spectroscopists because it displays a weak Jahn-Teller effect in its electronic ground state, combined with a strong spin-orbit interaction. In this work, we report an extension of the measurement of the pure rotational spectrum of the radical in its vibrational ground state in the submillimeter-wave region (350$-$860 GHz). CH$_3$O was produced by H-abstraction from methanol using F-atoms, and its spectrum was probed in absorption using an association of source-frequency modulation and Zeeman modulation spectroscopy. All the observed transitions together with available literature data in $v = 0$ were combined and fit using an effective Hamiltonian allowing to reproduce the data at their experimental accuracy. The newly measured transitions involve significantly higher frequencies and rotational quantum numbers than those reported in the literature ($f < 860$ GHz and $N \leq 15$ instead of 272 GHz and 7, respectively) which results in significant improvements in the spectroscopic parameters determination. The present model is well constrained and allows a reliable calculation of the rotational spectrum of the radical over the entire microwave to submillimeter-wave domain. It can be used with confidence for future searches of CH$_3$O in the laboratory and the interstellar medium.