Selected ion flow tube studies of the reactions of the isomers C 2H 5OH 2+ and (CH 3) 2OH + with a series of molecules

Abstract

The reactivities of the isomeric forms C 2H 5OH 2 + and (CH 3) 2OH + of C 2H 7O + with a series of molecules (C 2H 5OCHO, (CH 3) 2CHOH, CH 3CO 2H, CH 3C 6H 5, CH 3CHO, C 3H 4 (allene), CH 3OH, c-C 3H 6, H 2O and C 2H 6) having proton affinities ranging from 143.6 to 193.1 kcal mol −1 have been studied in a selected ion flow tube at 300 K. The reactivities of these species are generally consistent with the reaction energetics. When exothermic, proton transfer is a significant product channel for both isomers and the reactions proceed at close to the gas kinetic limit. When proton transfer is significantly endothermic, association is the only reaction mechanism with varying rate coefficients, but with the C 2H 5OH 2 + reaction being ≈ 50% more efficient than that for (CH 3) 2OH +. In cases with intermediate energetics, there are appreciable differences between the products and in the reactivities of these two isomers by as much as two orders of magnitude. Association is competitive with proton transfer in many cases and, for C 2H 5OH 2 +, channels are observed which can be viewed as initial association followed by ejection of H 2O. Such a mechanism is compatible with recent potential surface calculations which show that C 2H 5OH 2 + is closely coupled to the high energy proton bound dimer H 2O…H +…C 2H 4.