Submillimeter-Wave Spectroscopy of the CH₃O Radical

Area of Science:

• Chemical Physics
• Spectroscopy
• Astrochemistry

Background:

• The methoxy radical (CH3O) is a key molecule in atmospheric and interstellar chemistry.
• Its electronic ground state exhibits a weak Jahn-Teller effect and strong spin-orbit interaction, making it spectroscopically interesting.
• Previous studies provided limited spectral data, particularly in higher frequency regions.

Purpose of the Study:

• To extend the pure rotational spectrum measurement of the methoxy radical (CH3O) in its vibrational ground state.
• To improve the accuracy of spectroscopic parameters through extended frequency and quantum number measurements.
• To provide a reliable model for predicting the rotational spectrum across the microwave to submillimeter-wave range.

Main Methods:

• CH3O radicals were generated via H-abstraction from methanol using fluorine atoms.
• Submillimeter-wave absorption spectroscopy (350-860 GHz) was employed, utilizing source-frequency and Zeeman modulation.
• Observed transitions, combined with literature data, were fitted using an effective Hamiltonian.

Main Results:

• New transitions at significantly higher frequencies (up to 860 GHz) and rotational quantum numbers (N ≤ 15) were measured.
• The extended dataset led to significant improvements in the determination of spectroscopic parameters.
• A well-constrained spectroscopic model was developed, accurately reproducing existing and newly measured data.

Conclusions:

• The improved spectroscopic model allows reliable prediction of the CH3O rotational spectrum from microwave to submillimeter-wave frequencies.
• This work enhances the capability for detecting CH3O in laboratory experiments and astronomical observations.
• The study provides a foundation for future astrophysical and chemical physics research involving the methoxy radical.