A mass spectrometric study of positive and negative ion formation in an SF₆corona. I. Sources of sulphur-fluoride ions

Abstract

The mass spectra of positive ions generated in a positive high-voltage point-to-plane corona and negative ions generated in a negative high-voltage point-to-plane corona in high-purity SF6 are reported. In the absence of added impurities the major positively- and negatively-charged ions are SF5+, SF3+, SF2+, SF+, SF6-, SF5- and F-. Evidence for the formation of SF6 corona discharge neutral by-products, SF4 and SF2, is observed from the presence of cluster ions, SFx+(SF4) and SFx+(SF2), x=2, 3. Based on analyses of predicted ion intensities from cross-section data, SF2+ and SF+ ions are attributed to SF2 in the discharge, while most of the SF3+ observed is attributed to SF4. In the case of negative ions, analyses indicate that F- is formed in the discharge at high-density normalized electric field, E/N, from both dissociative attachment of SF6 and ion conversion processes, while SF6- and SF5- are likely to be formed outside the glow. Other ions observed resulting from the presence of trace contaminants include SOF3+, SOF2+, SOF+, SOF5- and F-(HF)2. In this paper (part I) the various sources of ions produced in 'pure' SF6 corona are discussed while in part II the effects of water and SF6 neutral corona by-products on ion formation are discussed.

Chemical ionization pathways of polyfluorinated chemicals—A connection to environmental atmospheric processes

“…It is interesting to note that it was not observed in the fragmentation of fluorinated acids, although it is recognized that this may be due to a lack of complexation of the species with the acid rather than it not being formed. The production of H 2 F 3 Ϫ appears to be even more novel, in terms of mass spectrometry, as it has only ever been reported once in literature concerning the identity of products in a high voltage point-to-point corona discharge [33].…”

Electron attachment to sulfur oxyhalides: SOF2, SOCl2, SO2F2, SO2Cl2, and SO2FCl attachment rate coefficients, 300–900 K

“…A number of literature articles describe such replacement reactions occurring in SF 6 discharges in air, motivated by the use of SF 6 as an insulator in electrical devices and the toxicity of the byproducts of reaction. [1][2][3][4] Neutral reactions involving O and F atoms have been observed to yield a variety of sulfur oxyfluorides in SF 6 / O 2 afterglows. [5][6][7][8] Surprisingly little work has been done on electron attachment to the sulfur oxyhalides.…”

Kinetics of Sulfur Oxide, Sulfur Fluoride, and Sulfur Oxyfluoride Anions with Atomic Species at 298 and 500 K

“…Hunton et al 9 measured the ratio of from S02-+ N is 41 kJ mol-' endothermic, which is roughly the SF 6 -and SF 5 -rate constants to be 5:1. In those experiments, energetically possible given the average thermal kinetic and an SF 5 -rate constant was determined to be 1.1 x 10-11 cm 3 rovibrational energy 57 -59 available in the SO2-+ N reaction system at 298 K. The reaction of S02-with N to generate O2-and HOSO isomers at the CCSD(T) level with several basis and NS is 151 Id mol-I endothermic, eliminating that possibility, sets. However, analogous calculations at these levels of theory These observations most likely indicate that the secondary for the HS02-anion structures are beyond the scope of the reaction of SO-with N is quite a bit faster than the S02-current study.…”

“…All of the SOxFy-ions react with 0; however, only SO2-reacts with both N and 0. SOFy--reactions with N (SO2-excluded) have a rate constant limit of < 1 x 10-" cm 3 s- 1 . The rate constants for the SOFy-reactions with H and 0 are _525% of the collision rate Introduction To both further the previous flow-tube studies of the oxidation chemistry of SOxF7-14, 15 and better understand the reactivity Sulfur dioxide (SO 2 ), sulfur fluoride (SF,-), and sulfur of these anions, the rate constants and product-ion branching oxyfluoride anions (SOxF0-) have been observed in plasma ratios for the reactions of SO,,Fy-ions with Hi, 112, N, N 2 , NO, environments where SF 6 , 02, and H 2 0 are present in the and 0 have been studied in a selected-ion flow tube (SIFT) at discharge.- 5 These ions have also been seen in atmospheric-298 K. The IH-atom reactions were also studied at temperatures pressure methane-oxygen flames doped with SF 6 and S0 2 .…”

“…6 7 up to 500 K. In addition, a series of theoretical calculations of Thus, the ion chemistry of these species has been studied to the structures and energetics of the possible H1SO 2 isomeric examine their reactivities. 5 1,-1 3 Recently, kinetics experiments species involved in the associative detachment reaction of SO,-have been conducted to determine the formation pathways for sies invole in toiatie detant tio ofsere these ions, particularly through oxidation by and with 11 were performed to better understand the observed Ethensie ton areticularly ccu ations ofbtheystructs ande chemistry. These results can be compared with the extensive Extensive theoretical calculations of the structures and energetics previous calculations of the neutral IISO 2 isomers created of these ions have augmented these measurements and have t 7 4 9 helped to explain the observed chemistry.…”