A time-of-flight mass spectrometry study of the fragmentation of valence shell ionised benzene

A time-of-flight mass spectrometry study has been carried out to investigate the fragmentation processes occurring in benzene as a result of valence shell photoionisation. Special emphasis has been placed on high energy reactions which lead to the formation of small energetic fragments. Synchrotron radiation has been used to record spectra in the photon energy range ~14-38 eV, and appearance energies have been determined for 20 fragment ions. The time-of-flight mass spectrometer has been designed such that the collection efficiency is independent of the fragment ion initial kinetic energy and mass. This feature has enabled reliable ion yield curves to be measured. Absolute photoionisation partial cross-sections for particular fragments have been obtained by combining the ion yield curves with the absolute photoionisation cross-section. The charge separation reaction: C₆H₆²⁺ ? CH₃⁺ + C₅H₃⁺ has been observed and the appearance energy has been measured as 27.8eV. Fragmentation rates have been determined by comparing the asymmetric time-of-flight peak shape of the C₃H₃⁺ fragment with the corresponding data obtained by ion trajectory modelling. © 2002 Elsevier Science B.V. All rights reserved.