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Negative surface ionization electron affinities and activation energies of SF n
Author(s) -
Chen Edward S.,
Chen Edward C. M.
Publication year - 2014
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.6804
Subject(s) - chemistry , thermal ionization , mass spectrometry , ionization , electron affinity (data page) , dissociation (chemistry) , ion , electron ionization , ionic bonding , electron , atomic physics , analytical chemistry (journal) , molecule , physics , organic chemistry , chromatography , quantum mechanics
RATIONALE Sulfur hexafluoride (SF 6 ) is the most frequently used standard for anion mass spectrometry because of its large temperature‐independent cross‐section for electron attachment. However, the kinetic and thermodynamic properties – the products of the reactions, and the number of negative ion states of the SF n – are presently in dispute. METHODS The electron affinities for SF n (n = 1–6) are predicted by assuming dissociation energies and ground‐state electron affinities based on literature values. The temperature dependence of the 2012 negative surface ionization mass spectrometer data, and other negative ionization mass spectrometry, electron capture detector, and beam and magnetron data, are analyzed using a kinetic model. RESULTS More precise and accurate activation energies for thermal electron attachment and electron affinities of SF 6 , SF 5 and SF 4 are reported. The largest experimental electron affinities of SF, SF 2 and SF 3 are assigned to the ground states. Ionic Morse potentials for multiple states are calculated. A mechanism for the formation of the ionic products observed in negative surface ionization thermal electron attachment to SF 6 is presented. CONCLUSIONS Negative surface ionization on a hot filament with mass spectrometry is a relatively simple and effective method for determining electron affinities similar to the electron capture detector, magnetron, swarm and beam procedures. A new method of predicting the number of negative ion states from dissociation limits establishes targets for the data analysis. Pseudo one‐dimensional anionic Morse potentials illustrate the mechanism for the reaction of thermal electrons with SF 6 and the consecutive dissociation pathways. Copyright © 2014 John Wiley & Sons, Ltd.