Photodissociation spectroscopy of (benzene-toluene)⁺. Charge delocalization in the hetero-dimer ion

The electronic spectrum of the benzene-toluene hetero-dimer ion is measured in the 380-1400 nm region. The spectrum shows intense bands around 1175 and 670 nm and a weaker band around 920 nm, which correspond to charge resonance (CR) bands of homo-dimer ions. The observation indicates that the positive charge stays on the benzene part in some probability, although the ionization potential of benzene is 0.4162 eV higher than that of toluene. A local excitation (LE) band is observed around 420 nm, where a π←π transition is locally excited in the charged benzene or toluene molecule. On the basis of the positions of the CR-like bands, as well as the intensity of the LE band relative to that of homo-dimer ions, the probability of finding the charge on the benzene molecule is analyzed to be approximately 36%.