Thermal decomposition of ethylbenzene cations (C8H10+): experiments and modeling of falloff curves

The kinetics of the pyrolysis of the ethylbenzene cation, C8H10+, has been studied in a turbulent ion flow tube (TIFT) from 623 to 673 K and at pressures from 30 to 250 Torr. The ions were prepared by the charge transfer reaction O2+ + C8H10 → O2 + C8H10+* followed by collisional stabilization and then by thermal decomposition in a nitrogen buffer gas. The thermal decomposition rate constants increased with temperature from about 15 to150 s−1, but did not vary with pressure, indicating the results refer to the high pressure limit. The experimental activation energy, 157.8 kJ mol−1, is similar to the bond energy value, 168.3 (±1.2) kJ mol−1, needed to model the data. Modeling of the system using a statistical adiabatic channel model/classical trajectory (SACM/CT) approach provided complete falloff curves for the dissociation and recombination of ethylbenzene. Similar modeling is also presented for the previously published data on n-propylbenzene cations. The temperature and pressure dependences of the rate coefficients for dissociation and recombination in the falloff range are represented in analytical form. The chosen format corresponds to that employed in data compilations for the corresponding neutral reaction systems.