Dynamics of the condensation reactions of C+ with C2H4 and C2H2

Abstract

The condensation reactions of C+ with C2H4 and C2H2 yielding new carbon–carbon bonds have been studied with crossed beam methods in the collision energy range from 0.5 to 1.5 eV. The data show that the reactions take place through short-lived collision complexes living a fraction of a rotational period. These results are shown to be consistent with schematic potential energy surfaces constructed from heats of formation and molecular structure calculations indicating that the large exothermicities of the reactions in comparison with the stabilities of intermediate C3H+4 and C3H+2 complexes should yield lifetimes in the 10−13 s regime. The data for C3H+2 formation from the reaction of C+ with C2H4 suggest two distinct production channels. These results are consistent with photoion-photoelectron coincidence breakdown curves for C3H+2 formation in the dissociative ionization of C3H4 isomers. The least exothermic reaction, C3H+ from reaction with ethylene, shows behavior in closest agreement with statistical predictions, specifically product kinetic energy distributions that scale with the total energy accessible to the products. This result is also in qualitative agreement with the nature of the potential energy surface mediating the reaction and lifetimes expected from the reaction energetics.