Cationic polymerization within van der Waals clusters of the form (CH₂=R)_n⁺ (R = CH₂, CF₂, and CHCH₃)

The cluster ion mass spectra resulting from electron ionization of van der Waals clusters composed of ethene, 1,1-difluoroethene (1,1-DFE), or propene molecules were observed as a function of expansion and ionization conditions. Expansion conditions favoring the formation of large neutral clusters lead to the observation of anomalous ion intensity distributions characterized by strong peaking as a function of cluster size. Comparisons are made between the present results and previous observations in both the gas and condensed phases. We propose that the anomalous cluster ion distributions arise as a consequence of the production of molecular (i.e., covalently bonded) ions produced by a series of intracluster addition (polymerization) reactions. The anomalous intensity distributions may then be accounted for in terms of kinetic bottlenecks in the addition reaction sequences which most likely result from the production of ions of low reactivity, most likely cyclic ions.