A photoionisation mass spectrometry study of the fragmentation of silicon tetrafluoride, tetrachloride and tetrabromide

摘要

A time-of-flight (TOF) mass spectrometry study has been carried out to investigate the fragmentation processes occurring in SiX_4 (X=F, Cl or Br). Synchrotron radiation has been used to record spectra in the photon energy range 10-210 eV, and appearance energies have been determined for 31 singly or doubly charged fragment ions. These have enabled upper limits for, previously unknown, heats of formation to be estimated for several doubly charged atomic and molecular fragments. The TOF spectra show that the peaks due to some of the small fragments change shape as a function of excitation energy, and that at high photon energy several of the peaks consist of two components, one of which is narrow and the other broad. The latter component is due to fragments possessing substantial initial kinetic energy. The peak shape is discussed in relation to the initial formation of a doubly or triply charged parent ion, and a subsequent Coulomb repulsion.