Molecular charge transfer reactions of monosubstituted benzenes at low energies

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Abstract
Cross sections for the symmetrical and exoergic asymmetrical charge transfer reactions of a series of monosubstituted benzenes were measured for primary‐ion kinetic energies between 30 and 150 eV. In this energy range, the charge transfer cross sections of all the reactions were found to be larger than the gas‐kinetic collisional cross sections, and their velocity dependence typical of resonant processes. These features seem to indicate that transitions to excited levels occur with high probability. The momentum transfer and the conversion of translational to internal energy in all the reactions was low, as expected for reactions having large impact parameters. In contrast to atomic and diatomic systems, no systematic difference was observed between symmetrical and asymmetrical processes, and molecular parameters other than the ionization potential of the system were found to affect the cross section. For a given projectile ion the cross section increased with the polarizability of the target molecule. This increase is associated with the deformation and lowering of the potential barrier. The nature of the projectile ion affected the magnitude of the cross section to about the same extent as did the target molecule, and this seems to be related to the energy defect of the reaction and to the dimensions and complexity of the projectile ion.