Abstract :
[en] The dissociation of benzylpyridinium “thermometer” ions is widely used
to calibrate the internal energy of ions produced in mass spectrometry. The
fragmentation mechanism is usually believed to yield a benzylium cation, although
recent studies suggest the possibility of a rearrangement leading to the tropylium isomer,
which would compromise the accuracy of energy calibrations. In this study, we used
IRMPD spectroscopy to probe the dissociation pathways of the p-(tert-butyl)-
benzylpyridinium ion. Our results show that the formation of both benzylium and
tropylium products is feasible depending on the activation regime and on the reaction
time scale. Varying the trapping delays in the hexapole gives insight into a rearrangement
mechanism occurring through consecutive reactions with an isomerization from
benzylium to tropylium. Our work provides experimental validations for the established
calibration procedure and highlights the adequacy of IRMPD spectroscopy to
qualitatively resolve gas-phase rearrangement kinetics.
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