Abstract
AbstractThe 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 [C7D8]+ and [C7D7]+ for toluene‐d8 and for the ion‐molecule reaction product [C8D9]+. PIE curves were modeled by k(E) dependences via RRKM/ QET calculations based on a model by Huang and Dunbar, with critical energy E0 = 2.13 eV and a 1000 K activation entropy ΔS≠ = −14.6 e.u. No energy range was found, even under long storage times, for which [C7D7]+ 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.
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