Electron Attachment Mass Spectrometry Research Articles

Decomposition Products and Mechanism of C5F10O/N2 Gas Mixture by Electron Attachment Mass Spectrometry

This work aims to detect the discharge products and study the decomposition characteristics of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> O/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas mixture under pulsed discharge. Discharge tests are carried out on three kinds of gas mixtures with different contents of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> O (3.3%, 10%, and 30%). Electron attachment mass spectrometry (MS) is proposed to detect discharge products after negative ionization, and the results are compared with that in gas chromatography (GC) MS. The discharge products are detected and the formation pathways of the main decomposition products are deduced. The results show that the densities of some products increase with the number of discharge pulses. There are differences on the types of products and the cumulative effect of discharge in the three kinds of gas mixtures. Furthermore, these discharge products are able to characterize the discharge accumulation effects in power switchgear, such as insulation degradation.

Detection of decomposition products of SF6/air gas mixture by electron attachment mass spectrometry

Sulphur hexafluoride (SF6) is widely used in gas insulation, and its decomposition products can be used to diagnose potential insulation failures. Quick and accurate detection of decomposition products can help to understand equipment-operating conditions in time. In this study, the decomposition products of SF6/air gas mixtures under different pulsed discharge voltages were studied. It was found that the main products were SOF2, SO2F2, SO2, CF4 and SOF4, and the yields of SOF2, SO2F2, SO2 and SOF4 increased with the number of discharge pulse. The productive rate of SOF2, SO2 and SOF4 were positively correlated with the discharge voltage, and when the discharge voltage increased from 5 to 15 kV, their yields after 50,000 discharges increased by 49%, 120% and 1100%, respectively. The productive rate of SOF2 and SO2 were positively correlated with the proportion of air in the gas mixtures while that of SOF4 was opposite. When the proportion of air increases from 0% to 90%, their yields after 50,000 discharges became 270%, 3169% and 10% of the originals, respectively. In addition, the productive rate of SO2F2 was not affected by discharge voltage and the proportion of air in the gas mixtures. SO2F2, SOF2, SOF4 and SO2 can be used as the basis for judging the discharge failures and the discharge degree of power equipment.

Detection and analysis of spark discharge products of C5F10O by electron attachment mass spectrometry

C5F10O has the potential to replace SF6 as an insulation gas in switchgears due to its high breakdown field strength and low global warming potential. However, as a newly synthesized gas, the chemical characteristics of C5F10O are not well known. In particular, the discharge products of C5F10O are not clear, which limits its insulating capability evaluation in long-term use, and further hinders the development of a gas sensor to monitor the insulation deterioration of C5F10O-containing switchgears. In this paper, electron attachment mass spectrometry (MS) was proposed to detect the decomposed products of C5F10O under pulsed spark discharge condition. It was found that the ionization source of the MS had an optimal electron energy of 2 eV to avoid decomposing the gas molecules to be detected while having a high detection sensitivity. The detected discharge products mainly included CF4, C2F4, C3F6, C3HF5, C3F8, C3HF7, C4F10, C5F10, C6F12, C3F4O and C2F6O, while CF4, C3HF5, C3HF7, C5F10, C6F12, C3F4O and C2F6O were not detected using GCMS. Based on the nonionization measurement, the decomposition mechanism was deduced. Also, it was found that the densities of some products, such as C3F6, C3F8, C4F10 were increasing with the discharge voltage and the number of discharge pulses, implying that these species might be used as indicators for the discharge accumulation effects such as the insulation deterioration of switchgears.

Reactions of C+ + Cl-, Br-, and I--A comparison of theory and experiment.

Rate constants for the reactions of C+ + Cl-, Br-, and I- were measured at 300 K using the variable electron and neutral density electron attachment mass spectrometry technique in a flowing afterglow Langmuir probe apparatus. Upper bounds of <10-8 cm3 s-1 were found for the reaction of C+ with Br- and I-, and a rate constant of 4.2 ± 1.1 × 10-9 cm3 s-1 was measured for the reaction with Cl-. The C+ + Cl- mutual neutralization reaction was studied theoretically from first principles, and a rate constant of 3.9 × 10-10 cm3 s-1, an order of magnitude smaller than experiment, was obtained with spin-orbit interactions included using a semiempirical model. The discrepancy between the measured and calculated rate constants could be explained by the fact that in the experiment, the total loss of C+ ions was measured, while the theoretical treatment did not include the associative ionization channel. The charge transfer was found to take place at small internuclear distances, and the spin-orbit interaction was found to have a minor effect on the rate constant.

Ab initio calculations of the dissociative attachment resonance energies for an octafluorocyclopentene molecule with comparisons to electron attachment mass spectrometric measurements

Dissociative electron attachment to an octafluorocyclopentene (c-C5F8) molecule has been investigated by means of ab initio molecular orbital calculations. Because of the antibonding character of the virtual valence orbitals, the temporary anions dissociate, producing neutral and negative radical fragments in reactive plasma. In order to identify the valence of virtual orbitals associated with the dissociative electron attachment in the calculation with the diffuse basis set, we examined the spatial distribution and antibonding characteristics of the virtual molecular orbitals. This theoretical approach reproduced experimental resonance energies of the dissociative electron attachment, which display rich resonance energy spectra as observed by electron attachment mass spectrometry.

Difference between C 4F 8 and C 5F 8 plasmas in surface reaction processes for selective etching of SiO 2 over Si 3N 4

Surface reactions induced by fluorocarbon plasmas were studied on SiO 2 and Si 3N 4 substrates using an inductively coupled plasma source. C 4F 8 and C 5F 8 were employed as source gases to investigate their differences in etching performance and selectivity on both SiO 2 and Si 3N 4 substrates. Polymer deposition was noticed in both gases by Fourier transform infrared ellipsometric measurements when substrate bias was not applied. When the bias was applied, etching started on the SiO 2 surface from a certain threshold bias voltage and the rate increased with the increase in voltage. However, on the Si 3N 4 surface this increasing tendency in C 5F 8 plasma was much less than that in C 4F 8 plasma. This difference provides a greater selectivity of SiO 2 to Si 3N 4 in C 5F 8 plasma. The reason for this increased deposition tendency in C 5F 8 plasma is attributed to the presence of higher mass species in a larger abundance than in C 4F 8 plasma, as confirmed by electron attachment mass spectrometry.

Diagnostics of polymerized species in processing plasmas by electron attachment mass spectrometry

Diagnostics of polymerized species in processing plasmas by electron attachment mass spectrometry

Electron attachment mass spectrometry as a diagnostics for electronegative gases and plasmas

Electron attachment mass spectrometry (EAMS) has been developed to study mixtures of electronegative gases and plasmas. A quadrupole mass spectrometer (QMS) has been used to detect negative ions, formed from sampled species by attachment of low energy electrons. Varying the electron energy allows to collect the attachment cross section of the considered species. EAMS appears to be a very powerful technique to study the chemistry of electronegative gases. Unlike ionization mass spectrometry, where cross sections are low at the threshold and rather flat over a broad range of electron energies, attachment resonances are sharp and distinct. Also very limited fragmentation of the parent negative ion occurs, so a given molecule yields only a few different negative ions. This facilitates identification of components in a gas mixture. It is particularly advantageous for detection of large, fragile molecules, which break up after ionization, but can be easily transformed into large negative ions. Moreover, sensitive detection of active species is possible due to their relatively high attachment cross sections. A particularly important application of EAMS is the determination of an effective attachment cross section in a plasma. Recording this cross section allows to decide on the actual negative ion formation mechanism in the plasma environment, where active products of plasma conversion can significantly alter the negative ion production channels and consequently the whole balance of charged particles. Examples of EAMS applications to fluorocarbon gases and low-pressure radio-frequency plasmas are discussed. In a CF4 discharge conversion of the parent gas into species like C2F6 and C3F8 is easily visualized. The dominant mechanism of negative ion formation in the plasma is electron attachment to these minority species and not to the parent gas. Also larger polymers are readily formed in fluorocarbon plasmas. In a C2F6 discharge molecules with up to ten carbon atoms (the mass limit of our apparatus) have been detected using EAMS.

Polymerization of fluorocarbons in reactive ion etching plasmas

Polymerization reactions in radio frequency fluorocarbon plasmas of CF4, C2F6, and C4F8 have been studied by electron attachment mass spectrometry (EAMS). In these plasmas polymerization occurs readily and molecules containing up to ten carbon atoms (the mass limit of the mass spectrometer) have been found. The densities of large polymers increase with increasing size of the parent gas. In a fluorine-rich environment like a CF4 plasma the detected polymers are mainly fully saturated with F (CnF2n+2). As the amount of fluorine in the parent gas decreases, also the degree of saturation of the polymers decreases, which is clearly seen in C2F6 and C4F8 plasmas. The unsaturated polymers are more reactive, so they can stick more easily to surfaces and possibly create thick polymer films, which are often observed after discharge operation. The polymerization rate depends on the chemical activity of the plasma, which can be easily enhanced by increasing the radio frequency power. The positive ions, extracted from the plasma, are generally somewhat smaller than the neutral polymers and their fluorine content is lower. This is probably due to dissociation of neutrals during their ionization by plasma electrons and to ion collisions in the sheath region. Finally, we have shown that EAMS has considerable advantages in the study of electronegative plasmas and polymerization processes in comparison with traditional mass spectrometry. Unlike the traditional mass spectrometry, employing ionization by high energy electrons, EAMS much better preserves the structure of high polymers, allowing us to detect them as large negative ions.

Electron Attachment Mass Spectrometry for the Detection of Electronegative Species in a Plasma

Electron attachment mass spectrometry (EAMS) has been implemented to detect electronegative species in a low pressure 13.56 MHz discharge. For this purpose a source of low energy electrons has been used in combination with a quadrupole mass spectrometer (QMS) and the signal of the negative ions, resulting from electron attachment to neutrals has been recorded as a function of the electron energy. Chemically active fluorocarbon gases like CF4 and CHF3 have been studied. EAMS provides much insight into chemistry in the plasma, especially into mechanisms of negative ion formation. It enables the detection of electronegative species, formed from the parent gas under plasma conditions, based on their different attachment cross sections. Moreover, the effective negative ion formation cross section in a plasma, taking into account the chemical conversion of the feed gas, can be determined. In fluorocarbon plasmas various species are formed, like C2F6 and C3F8 in a CF4 plasma and CF4 and C2F6 in a CHF3 plasma, which significantly influence the negative ion production mechanisms under discharge conditions. Because the active neutrals produced in the plasma have typically both a larger attachment cross section and a lower attachment energy threshold, negative ion formation is dominated by the plasma species and not by the parent gas.

Mass spectrometry of perfluoroalkylated Buckminsterfullerene: a case for sequential gas phase double electron capture

Electron attachment mass spectra of the products of fluoroalkyl radical additions to C 60 show intense molecular ions as well as ions produced by attachment of two electrons to the gas phase molecules. Remarkably, little fragmentation is observed for these fluorocarbon derivatized fullerenes, suggesting that electron attachment is occurring on the highly electron deficient C 60 rather than the fluorocarbon side chains. Perfluoroalkylated C 60 compounds are sufficiently volatile to be used as mass references for high-mass electron attachment mass spectrometry. These compounds are also found to produce molecular ions by negative ionization matrix assisted laser desorption ionization mass spectrometry.

Occurrence and fragmentation of high-mass fullerenes

Extracts of graphitic soot are shown by electron attachment mass spectrometry to contain, in addition to the well-known fullerenes C 60 and C 70, smaller quantities of larger carbon clusters, up to C 200. A structure for one of the more abundant clusters, C 76, is proposed. The data show the conspicuous absence of particular clusters. The relative stabilities of C 60, C 70 and C 84 were investigated by charge exchange and collision activated dissociation experiments. All the fullerene ions showed remarkable stability to fragmentation. At the highest collision energies accessible, fragmentation of C 2+ 70 and C − 70 produced a series of products from C 2 loss, including the conspicuous formation of C 60 ions.

ChemInform Abstract: INVESTIGATIONS INTO AROMATIC HYDROCARBONS AND THEIR NITROGEN AND SULFUR HETERO ANALOGS BY MEANS OF ELECTRON ATTACHMENT MASS SPECTROMETRY

Chemischer InformationsdienstVolume 8, Issue 37 Physical Organic Chemistry ChemInform Abstract: INVESTIGATIONS INTO AROMATIC HYDROCARBONS AND THEIR NITROGEN AND SULFUR HETERO ANALOGS BY MEANS OF ELECTRON ATTACHMENT MASS SPECTROMETRY G. ALBERS, G. ALBERSSearch for more papers by this authorH. KNOF, H. KNOFSearch for more papers by this author G. ALBERS, G. ALBERSSearch for more papers by this authorH. KNOF, H. KNOFSearch for more papers by this author First published: September 13, 1977 https://doi.org/10.1002/chin.197737047AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume8, Issue37September 13, 1977 RelatedInformation

Untersuchungen von aromatischen Kohlenwasserstoffen sowie von N- und S-Heteroanalogen mit Hilfe der Elektronen- anlagerungsmassenspektrometrie / Investigations into Aromatic Hydrocarbons and N and S Heterocompounds thereof by Means of Electron Attachment Mass Spectrometry

Abstract Investigations into Aromatic Hydrocarbons and N and S Heterocompounds thereof by Means of Electron Attachment Mass Spectrometry Aromatic compounds as well as their nitrogen and sulphur heterocompounds with molecular weight M&gt;100 are investigated using negative ions from electron attachment mass spectrometry. Mass spectra of aromatic compounds produce molecular peaks as basepeaks predominantly. In general, the type of the basepeak of heterocompounds and its detection sensitivity depends more on the chemical structure of the compound than on the type of the heteroatom. The relative detection sensitivity of the molecular peak in dependence of an amount of sample is a linear function on a log-log scale. Addition of argon extends this linear dependence towards larger sample amounts. For quantitative analysis, however, the measurements must be performed at a fixed ion source pressure.