Acetylene electron impact

Verification of the molecular weight of thiirene dioxides by mass spectrometry, employing the conventional electron-impact (El) ionization method, has been unsuccessful due to the absence or insignificant intensity of molecular ion peaks in their mass spectra. The base peak is rather characteristic, however, and corresponds to the formation of the disubstituted acetylene ion by loss of sulfur dioxide91 (equation 3). 

Schwarz, H. Koppel, C. Bohlmann, F. Electron Impact-Induced Fragm tation of Acetylene Compounds. XII. Rearrangement of Bis(Trimelhylsilyl) Ethers of Unsaturated a,G)-Diols and Mass Spectrometric Identification of Isomeric Ph ols. Tetrahedron 1974, 30, 689-693. 

Hydrocarbon molecules are abundant constituents of planetary atmospheres and major compounds in combustible gas mixtures and in fusion edge plasmas [7-11]. Methane is the simplest of these hydrocarbon molecules. Acetylene, C2H2, is the simplest hydrocarbon molecule that contains 2 carbon atoms. Thus absolute total and partial photon [24-27] and electron [15,28-34] ionization cross-sections and nascent fragment ion energy distributions [19,20,28,36-40] have been studied extensively for these molecules. For the deuterated methane molecule electron impact ionization and dissociative ionization cross-sections were determined for the CD (x=l—4) molecule and radicals applying a fast neutral beam technique [41]. Electron impact total ionization cross-sections have been determined also theoretically applying the BEB (Binary-Encounter-Bethe) model [42], the DM (Deutsch-Mark) method [43] and the JK (Jain-Khare) method [44], Partial electron impact ionization cross-sections were calculated for methane [45,46] as well as total electron impact cross-sections for various CH radicals [47]. The dissocia-... 

Fig. 20.7. The upper panel shows the ion beam profiles of the C+ and H+ fragment ions in the z-direction, produced by electron impact ionization of methane and acetylene at an electron energy of 100 eV. The ion signal was measured as a function of the voltage on the z-deflector pair. In the lower diagram the initial kinetic energy distributions are displayed that were calculated from the z-profiles shown above. The initial kinetic energy distribution of both fragment ions consist of two parts designated as thin lines. The sum of the two contributions represents the total initial kinetic energy distribution and is displayed as a thick line in the same line style...

The only pyrylium benzologue for which mass spectral data are available is the flavylium ion (12) (69AK(30)393>. On electron impact, (12) forms a highly stable molecular ion as the base peak which decomposes by two pathways (Scheme 27). Pathway A generates the [M-H]+ ion (12a). There is some evidence to suggest thaft loss of CO from (12a) gives the phenanthrene radical ion (12b) (m/e 178). Subsequent ejection of an acetylene molecule generates the biphenylene ion (12c). 

The electron beam produces free radicals as well as cations. Neutral radicals tend not to isomerize (or, if they do, they rearrange by pathways different from those of cations). As a result, the neutral products from cationic rearrangements can generally be distinguished from the ones that arise via neutral free radicals. To judge from the relative abundances of neutral products recovered from the EBFlow, 70 eV electron impact produces more cations than radical pairs. Only very light hydrocarbons (e.g. ethylene and acetylene) are formed in yields comparable to the yields of cationic products. 

Acetylene is also one of the systems for which mass spectrometric investigations of ion—molecule reactions have been most extensively carried out [134, 152, 201, 238, 240, 305—311]. Primary ions obtained by ordinary electron impact on acetylene are essentially and... 

This chapter is divided into three sections. Section 1 covers the electron ionization (El) mass spectra of acetylenic compounds and discusses the types of singly and doubly charged cations formed on electron impact. Section 2 concerns the unimolecular chemistry of ions with C=C bonds. Finally, Section 3 is devoted to the ion-molecule reactions of acetylenic ions and acetylenes. The material mainly originates from articles that have been published within the last decade and is presented with considerable detail. This review does not claim to be exhaustive nevertheless, it provides examples from all areas of active mass spectrometry research in C=C bonded molecules, so that the reader can learn about the important and novel developments in this area. 

This change in E/N as methane is replaced with acetylene strongly influences the EVDF, as shown in figure 12. As a result of this, kinetics of electron impact plasma chemical reactions is not the same at different precursors as well as at different region along the axis of tubes. 

Fig. 14. Variation in the rate constants for electron impact acetylene dissociation, methane dissociation, argon ionization and argon metastables formation along the axis of the tube.

Chemical kinetics of methane and acetylene dissociation and other gas phase reactions are studied for him coating applications under atmospheric pressure plasma conditions. In order to determine the plasma parameters, OES, V-I measurement, micro-photography and numerical simulations are used. From the determined EVDF and n, electron impact plasma chemical reaction rates are determined. On the basis of rate of different possible reaction. 

Electron-impact-induced fragmentations of simple acetylenes and aa -diacetylenic ketones have been reported, and also the infrared spectra of various acetylenic derivatives of arsenic. ... 

Tate, IT, Smith, RT, and Vaughan, A.L. (1935) A mass spectrum analysis of the products of ionization by electron impact in nitrogen, acetylene, nitric oxide, cyanogen and carbon monoxide. Physical Review, 48,525-531. 

The loss intensities are a strong function of the incident electron energy and only average values are reported here. This could be due to molecular resonances or short range "impact" scattering ( , 9, 1(), 96) as discussed by Lehwald and Ibach for the case of acetylene chemisorbed or Ni(lll)... 

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