Unimolecular Fragmentation of the Toluene Molecule Ion

Using a pulsed ion source in which the time between ion formation and ion withdrawal for analysis can be varied, the unimolecular fragmentation of the toluene molecule ion $${\mathrm{C}}_7{\mathrm{H}}_8^{+}\to {\mathrm{C}}_7{\mathrm{H}}_7^{+}+\mathrm{H}$$ has been studied. The results indicate that the major part of the fragmentation occurs from a state or states with a half‐life of 0.1 μsec or less. However, a significant fraction of the toluene ions decompose from a state with a half‐life of approximately 5 μsec. Studies with deuterium‐labeled toluenes indicate extensive scrambling of the ring and methyl hydrogens in both the ``fast'' and ``slow'' reactions. The isotope effect in the ``fast'' reaction is quite small, however, for the ``slow'' reaction k_H/k_D=3.6.