Assessing the Viability of the Methylsulfinyl Radical-Ozone Reaction

Area of Science:

• Atmospheric Chemistry
• Theoretical Chemistry
• Computational Chemistry

Background:

• The reaction of methylsulfinyl radical (CH3SO) with ozone is crucial for remote marine atmospheric sulfur chemistry.
• Previous theoretical studies reported an unusually high energy barrier for this reaction, posing challenges for accurate modeling.

Purpose of the Study:

• To accurately characterize the potential energy surface for the reaction between methylsulfinyl radical (CH3SO) and ozone.
• To correct the unphysically large barrier reported in prior theoretical investigations.

Main Methods:

• Density Functional Theory (DFT) was employed to characterize the potential energy surface.
• Multireference methodologies, including complete active-space self-consistent field (CASSCF), were utilized.
• The study identified and analyzed the reaction pathway, including intermediate adducts and transition states.

Main Results:

• The reaction proceeds via an addition adduct [CH3S(O3)O] with a deep potential well (-37 kcal/mol).
• Dissociation of the adduct occurs with a low barrier (1 kcal/mol) to form CH3SO2 + O2.
• Multireference computations indicate the initial addition of CH3SO + O3 is barrierless, contradicting previous findings.

Conclusions:

• The reaction between CH3SO and ozone is more facile than previously thought, with a low overall energy barrier.
• The calculated pathway provides a more physically accurate representation of the reaction mechanism.
• The CH3SO2 product can readily decompose to sulfur dioxide (SO2), consistent with known atmospheric sulfur chemistry.