MASS-SPECTROMETRIC STUDY OF THE IONIZATION AND DISSOCIATION OF SULFUR-HEXAFLUORIDE BY MONOENERGETIC ELECTRON-IMPACT

The ionization and fragmentation of SF6 under electron impact has been examined by means of a trochoidal electron velocity selector and a ma ss spectrometer. The ionization efficiency curves of the positive ions were recorded and the appearance energies of different electronic sta tes of these ions were determined. The experimental results were combi ned with auxiliary thermochemical data to evaluate the dissociation en ergies D circle degrees(F5S-F) = 4.01 eV, D degrees circle(F4S-2F) = 6 .39 eV, D degrees circle(F3S-3F) = 9.98 eV, the ionization energy of S F5, = 11.27 eV and heats of formation Delta H degrees(f)(SF5+) = 1.81 eV, Delta H degrees(f)(SF4+) = 4.12 eV, Delta H degrees(f)(SF3+) = 4.1 1 eV and Delta H degrees(f)(SF3) = - 5.13 eV. (C) 1998 John Wiley & So ns, Ltd.