Abstract
Gas-phase ion-molecule reactions in ethene were measured by using a pulsed-electron beam high-pressure mass spectrometer. All the major ions observed, i.e., C2H3+, C2H4+, and C2H5+, were found to react with C2H4 to form polymerized ions. The degree of polymerization increased with decrease of temperature. This is due to the presence of the entropy barrier in the reaction coordinate. When the ethene pressure was increased, the polymerization reactions were greatly suppressed. This is due to the steric hindrance for the polymerization reaction by the formation of cluster ions, i.e., the entropy bottle neck for the formation of polymerized ions becomes narrower by the formation of cluster ions. The chemical reactivity of C2H3+ was found to be the smallest among three carbocations.
