Unconventional atomic-level mechanism induced by a submerged saddle in the O(¹D) + CH₃OCH₃ reaction

Elucidating the mechanisms of excited-state atom reactions with hydrocarbons and their derivatives is important for the study of interstellar and combustion chemistry. For these reactions, atom insertion into chemical bonds is the acknowledged pathway, however, this concept could be invalid. Here, through a combined experimental and theoretical study of the O(¹D) + CH₃OCH₃ reaction, we demonstrate that the accepted insertion mechanisms, including O-insertion into C-O bonds, do not occur, and reveal an unconventional atomic-level mechanism, designated as O+H-C collision activation stereocyclization, that supersedes O-insertion into C-H bonds. Dynamics calculations, performed on a high-level ab initio potential energy surface, yield rate coefficients in very good agreement with experiment, exhibiting an unexpected increase with temperature. This finding is attributed to an unusual submerged saddle as part of the unconventional mechanism. As this mechanism probably exists in other excited-state atom reactions, the dynamical effects uncovered here are expected to have general significance.