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Time‐dependent mass spectra and breakdown graphs: 15—toluene‐ d 8
Author(s) -
Ohmichi N.,
Gotkis I.,
Steens L.,
Lifshitz C.
Publication year - 1992
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210270407
Subject(s) - chemistry , ion , photoionization , dissociation (chemistry) , kinetic energy , ionization , atomic physics , internal energy , toluene , mass spectrum , mass spectrometry , ion trap , spectral line , analytical chemistry (journal) , bond dissociation energy , physics , organic chemistry , chromatography , quantum mechanics , astronomy
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.