Charge separation reactions of doubly charged benzene ions

Photoion-photoion coincidence spectra of benzene and benzene-d₆ photoionized by He(II) light and synchrotron radiation show the existence of six major and eight minor charge-separation reactions of the [C₆H₆]²⁺ ion. Three main groups of ion pairs are related to [C₃H₃]⁺ + [C₃H₃]⁺, [C₂H₃]⁺ + [C₄H₃]⁺ and [CH₃]⁺ + [C₅H₃]⁺, with appearance energies of 32.2 ± 0.5 eV, 31.3 ± 0.5 eV and 28.4 ± 0.3 eV. The kinetic energy release is the same for all pairs within a group, irrespective of hydrogen number, but differs from group to group. Results are interpreted in terms of fast, direct charge separation of [C₆H₆]²⁺, and subsequent hydrogen loss by the singly charged fragments.