The methylsulfinyl radical CH3SO examined

Area of Science:

• Atmospheric Chemistry
• Quantum Mechanics
• Computational Chemistry

Background:

• The methylsulfinyl radical (CH3SO) is a critical intermediate in marine atmospheric chemistry, influencing the oxidation of dimethyl sulfide.
• Previous studies have investigated CH3SO using various quantum mechanical methods.

Purpose of the Study:

• To perform high-level ab initio quantum mechanical computations for the ground (X̃ ²A″) and first excited (Ã ²A') electronic states of the methylsulfinyl radical.
• To accurately determine the structural parameters, energy differences, and vibrational frequencies of these electronic states.

Main Methods:

• Utilized advanced ab initio quantum mechanical methods, including CCSDT(Q).
• Employed large basis sets, up to cc-pV(5+d)Z.
• Calculated ground and excited electronic state properties.

Main Results:

• Reported significantly different S-O bond distances for the X̃ ²A″ (1.499 Å) and à ²A' (1.652 Å) states.
• Predicted an X̃ to à adiabatic energy difference of 45.1 kcal mol⁻¹, substantially higher than the analogous methylperoxy radical (21.1 kcal mol⁻¹).
• Calculated the internal rotation barrier (0.92 kcal mol⁻¹) and torsional vibrational frequencies (142 cm⁻¹ harmonic, 128 cm⁻¹ anharmonic) for the X̃ ²A″ state. First vibrational frequencies for the à ²A' state are reported.

Conclusions:

• The study provides highly accurate computational data for the methylsulfinyl radical's electronic states.
• These findings enhance our understanding of CH3SO's role in atmospheric oxidation processes.
• The reported vibrational frequencies for the excited state are novel and contribute to spectral characterization.