Revealing new pathways for the reaction of Criegee intermediate CH 2 OO with SO 2 .

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 CH 2 OO + SO 2 system and reveal how the reaction happens step by step by quasi-classical trajectory simulations. A new pathway forming the main products (CH 2 O + SO 3 ) and a new product channel (CO 2  + H 2  + SO 2 ) 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 OCH 2 O ∙ ∙ ∙ SO 2 is formed first, and then in most cases it soon turns into HCOOH + SO 2 , in a few cases it decomposes into CO 2  + H 2  + SO 2 which is a new product channel, and rarely it remains as ∙OCH 2 O ∙ + SO 2 .