New insights into the mechanism and kinetics of the addition reaction of unsaturated Criegee intermediates to CF 3 COOH and tropospheric implications.

In this work, we have investigated the mechanism, thermochemistry and kinetics of the reaction of syn - cis -CH 2 R z CR y CO + O - (where R z , R y = H, CH 3 -) unsaturated Criegee intermediates (CIs) with CF 3 COOH using quantum chemical methods. The rate coefficients for the barrierless reactions were calculated using variable reaction coordinate variational transition state theory (VRC-VTST). For the syn - cis -CH 2 R z CR y CO + O - conformation in which conjugated CC and CO double bonds are aligned with each other, we propose a new pathway for the unidirectional addition of an OC-OH molecule (CF 3 COOH) to the CC double bond of syn - cis -CH 2 R z CR y CO + O - . The rate coefficient for the 1,4-CC addition reaction at 298 K is ∼10 -10 to 10 -11 cm 3 s -1 , resulting in the formation of CF 3 C(O)OCH 2 CR z R y COOH trifluoroacetate alkyl allyl hydroperoxide (TFAAAH) as a new transitory adduct. It can act as a precursor for the formation of secondary organic aerosols (SOAs). This novel TFAAAH hydroperoxide was identified through a detailed quantum chemical study of the 1,4-addition mechanism and will provide new insights into the significance of the 1,4-addition reaction of unsaturated Cls with trace tropospheric gases on -CR z CH 2 vinyl carbon atoms.