Variationally Computed IR Line List for the Methyl Radical CH₃.

Area of Science:

• Computational Chemistry
• Molecular Spectroscopy
• Quantum Mechanics

Background:

• Accurate spectroscopic data for small molecules like the methyl radical (CH3) are crucial for various scientific fields.
• Previous line lists may not cover the high-temperature regimes relevant for astrophysical and combustion chemistry.

Purpose of the Study:

• To compute the first hot-temperature, ab initio spectroscopic line list for the CH3 radical.
• To provide accurate ro-vibrational energy levels and Einstein A coefficients for CH3.

Main Methods:

• Utilized a high-level ab initio potential energy surface and dipole moment surface for CH3.
• Employed the general-molecule variational approach within the TROVE computer program.
• Calculated ro-vibrational energy levels and Einstein A coefficients.

Main Results:

• Generated a comprehensive line list with over 9 million ro-vibrational states and 2 billion transitions.
• Calculated spectral properties cover wavenumbers up to 10,000 cm⁻¹.
• Vibrational energies and intensities show excellent agreement with experimental data.

Conclusions:

• The computed line list is suitable for high-temperature applications (up to 1500 K).
• This work provides a valuable resource for atmospheric and combustion studies involving the CH3 radical.