LAUSR

Abstract Mechanisms and reaction channels of the CHBr 2 and CBr 3 with NO 2 reactions have been studied by quantum chemistry methods. The calculated results indicating that the title reactions can take place on either the singlet or triplet potential energy surfaces (PES) and the pathways on the triplet PES should be much less competitive than that on the singlet PES. On the singlet surface, CHBr 2 radical can associate with NO 2 to barrierlessly generate adduct IM1 (CHBr 2 NO 2 ), followed by isomerization to IM2a ( trans–cis -CHBr 2 ONO) and IM2b ( trans – trans -CHBr 2 ONO), which can easily interconvert to IM2c and IM2d. Starting from IM2 (IM2a, IM2b, IM2c and IM2d), the most favorable channel involves the 1,3-Br migration along with N O bond rupture of IM2a leading to P1 (CHBrO + BrNO), or the 1,4-Br shift accompanied by the N O bond cleavage of IM2d to form P5 (CHBrO + BrON). Moreover P1 and P5 can further dissociate to generate P6 (CHBrO + NO + Br). Much less competitively, IM2a could take the 1,3-H-shift associated with the N O bond cleavage to give product P2 (CBr 2 O + HNO). Due to highly energy barriers and unstable products, the pathways of formation other products could be neglected. For the singlet potential energy surface of CBr 3  + NO 2 reaction, the only dominant product is found to be P1 (CBr 2 O + BrNO), which can direct rupture N-Br single bond of BrNO to form the secondary product P2 (CBr 2 O + NO + Br). The present study may be helpful for further experimental investigation of the title reactions.