Spectroscopy and excited-state dynamics of benzene-trimer ion

The photodissociation of (C₆H₆)₃ ⁺ is studied in the range hν = 0.9-3.0 eV. The electronic spectrum of (C₆H₆)₃ ⁺ shows the main band at hν ≈ 1.29 eV and a side band at ≈ 1.02 eV. The (C₆H₆)₃ ⁺ ion retains spectroscopic features characteristic of (C₆H₆)₂ ⁺, suggesting that the positive charge is carried by a dimer subunit in (C₆H₆)₃ ⁺. The major fragment ion changes smoothly from (C₆H₆)₂ ⁺ to C₆H₆ ⁺ with increasing photon energy from 0.9 to 1.8 eV. The product branching ratios and the kinetic energy of the C₆H₆ ⁺ fragment are consistent with a two-step model for the formation of C₆H₆ ⁺.