The dissociative ionization of ethylene dimers, trimers, and tetramers studied by photoelectron photoion coincidence

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Abstract
The dissociation dynamics of energy selected ethylene dimer ions is investigated by photoelectron photoion coincidence. The derived dissociation rates as a function of the ion internal energy were found to be identical to those previously measured for rotationally cold C4H+8 ions. This demonstrates that the ethylene dimer ions rearrange to the 2-butene isomers prior to dissociation. The ethylene dimer ions are produced by ionization of neutral ethylene dimer as well as by dissociative ionization of the neutral trimer. The statistical theory analysis of the kinetic energy released in the dissociative photoionization of the ethylene trimers indicates that these ions dissociate to the 2-butene ion. At the energies investigated, the evaporation of a single monomer unit from the trimer ion removes sufficient energy to prevent further dissociation of the C4H+8 ions. All of the ethylene trimer ion signal was a result of dissociative ionization of higher order clusters. Finally, we show that the ethylene tetramer ion evaporates an ethylene unit as the core polymerizes to a straight chain hexene ion.