Time‐dependent mass spectra and breakdown graphs: 15—toluene‐ d 8

The ion storage time in the cylindrical trap of a pbotoionization mass spectrometer has been extended to ∼500 ms. Time‐resolved photoionization efficiency (PIE) curves were meaured for [C 7 D 8 ] + and [C 7 D 7 ] + for toluene‐ d 8 and for the ion‐molecule reaction product [C 8 D 9 ] + . PIE curves were modeled by k ( E ) dependences via RRKM/ QET calculations based on a model by Huang and Dunbar, with critical energy E 0 = 2.13 eV and a 1000 K activation entropy Δ S ≠ = −14.6 e.u. No energy range was found, even under long storage times, for which [C 7 D 7 ] + is pure tropylium, Tr + . The results are interpreted via the case C behaviour in isomerizing ions, due to Baer and co‐workers, according to which Tr + and [benzyl] + , Bz + , are formed at equal rates for energies in excess of both of their dissociation limits. Dissociation is suppressed at internal energies lower than ∼2.S eV due to radiative decay in the infrared region. Dissociations observed at photon energies lower than ∼11.3 eV (8.8 eV ionization energy +2.5 eV internal energy) are ascribed to the offsetting effects of an intrinsic kinetic shift of ∼0.4 eV and the thermal energy distribution in the molecular ions.