Mass spectrometric study of the ionization and dissociation of sulphur hexafluoride by monoenergetic electron impact
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The ionization and fragmentation of SF6 under electron impact has been examined by means of a trochoidal electron velocity selector and a mass spectrometer. The ionization efficiency curves of the positive ions were recorded and the appearance energies of different electronic states of these ions were determined. The experimental results were combined with auxiliary thermochemical data to evaluate the dissociation energies 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 SF5, = 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+) = 4.11 eV and Delta H degrees(f)(SF3) = - 5.13 eV. (C) 1998 John Wiley and Sons, Ltd.