Revealing new pathways for the reaction of Criegee intermediate CH₂OO with SO₂

Criegee intermediates play an important role in the tropospheric oxidation models through their reactions with atmospheric trace chemicals. We develop a global full-dimensional potential energy surface for the CH₂OO + SO₂ system and reveal how the reaction happens step by step by quasi-classical trajectory simulations. A new pathway forming the main products (CH₂O + SO₃) and a new product channel (CO₂ + H₂ + SO₂) are predicted in our simulations. The new pathway appears at collision energies greater than 10 kcal/mol whose behavior demonstrates a typical barrier-controlled reaction. This threshold is also consistent with the ab initio transition state barrier height. For the minor products, a loose complex OCH₂O ∙ ∙ ∙ SO₂ is formed first, and then in most cases it soon turns into HCOOH + SO₂, in a few cases it decomposes into CO₂ + H₂ + SO₂ which is a new product channel, and rarely it remains as ∙OCH₂O ∙ + SO₂.