Reactions of H₃O⁺ and H₂O⁺ with Several Fully Halogenated Bromomethanes

Abstract

The bimolecular rate coefficients and ion products for the reactions of H 3 O + and H 2 O + with the brominecontaining molecules CF 3 Br, CF 2 Br 2 , CF 2 BrCl, CFBr 3 , CFBr 2 Cl, and CBrCl 3 at 300 K are reported. With the exception of the reactions of H 3 O + with CF 3 Br and CF 2 BrCl, the rate coefficients are near the collisional values (k ≈ 10 -9 cm 3 molecule -1 s -1 ). The most efficient exit pathway for the majority of the H 3 O + reactions is the formation of a trihalomethyl cation, together with water and a hydrogen halide as the neutral products. In each case, more than one trihalomethyl cation can be formed. The branching ratios are largest for the products resulting from the breaking of a C-F bond. This is attributed to the high bond strength of HF relative to HCl and HBr. Similarly for CBrCl 3 , the major product cation is CCl 2 Br + . The H 2 O + reactions are found to proceed predominantly via charge transfer. For the reaction of H 2 O + with CF 3 Br there is clear evidence for intimate reaction pathways in which bonds are broken and formed.