SELECTED-ION FLOW TUBE STUDIES OF THE REACTIONS OF THE ISOMERS C2H5OH2+ AND (CH3)(2)OH+ WITH A SERIES OF MOLECULES

The reactivities of the isomeric forms C2H5OH2+ and (CH3)(2)OH+ of C2H 7O+ With a series of molecules (C2H5OCHO, (CH3)(2)CHOH, CH3CO2H, CH3C6 H5, CH3CHO, C3H4 (allene), CH3OH, c-C3H6, H2O and C2H6) 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 specie s are generally consistent with the reaction energetics. When exotherm ic, proton transfer is a significant product channel for both isomers and the reactions proceed at close to the gas kinetic limit. When prot on transfer is significantly endothermic, association is the only reac tion mechanism with varying rate coefficients, but with the C2H5OH2+ r eaction being approximate to 50% more efficient than that for (CH3)(2) OH+. In cases with intermediate energetics, there are appreciable diff erences between the products and in the reactivities of these two isom ers by as much as two orders of magnitude. Association is competitive with proton transfer in many cases and, for C2H5OH2+, channels are obs erved which can be viewed as initial association followed by ejection of H2O. Such a mechanism is compatible with recent potential surface c alculations which show that C2H5OH2+ is closely coupled to the high en ergy proton bound dimer H2O ... H+... C2H4. (C) 1997 Elsevier Science B.V.