Impact investigation, fragments

During the last decade knowledge of the ion chemistry of nitro compounds in the gas phase has increased significantly, partly due to the more widespread use of specialized techniques. Thus various ionization methods, in particular electron impact ionization and chemical ionization, have been used extensively. In addition, structure investigations as well as studies on fragmentation pathways have involved metastable ion dissociations, collision activation and neutralization/reionization studies, supplementary to studies carried out in order to disclose the associated reaction energetics and reaction dynamics. In general, the application of stable isotopes plays a crucial role in the in-depth elucidation of the reaction mechanisms. 

There are a number of other methods for ionising the sample in a mass spectrometer. The most important alternative ionisation method to electron impact is Chemical Ionisation (Cl). In Cl mass spectrometry, an intermediate substance (generally methane or ammonia) is introduced at a higher concentration than that of the substance being investigated. The carrier gas is ionised by electron impact and the substrate is then ionised by collisions with these ions. Cl is a milder ionisation method than El and leads to less fragmentation of the molecular ion. 

In connection with a study of the electron impact-induced fragmentations of 1,2,3-thiadiazoles, the mass spectrum of 5-phenylthiatriazole has been scrutinized.13 Jensen et al.1 have undertaken a detailed investigation including 5-aryl-, 5-amino-, and 5-alkylthiothiatriazoles. The electron impact-induced decompositions resemble the pyrolytic loss of N2S (Section III, A). In all cases the M—N2S ion together with its fragmentation is responsible for the major part of the total ion current. A detailed discussion of the spectra is outside the scope of this review. 

A.D. Salman, C.A. Biggs, J. Fu, I. Angyal, M. Szabo, M.J. Hounslow, An experimental investigation of particle fragmentation using single particle impact studies, Powder Technol. 128 (2002) 36-46. 

Analytical pyrolysis is defined as the characterization of a material or a chemical process by the instrumental analysis of its pyrolysis products (Ericsson and Lattimer, 1989). The most important analytical pyrolysis methods widely applied to environmental samples are Curie-point (flash) pyrolysis combined with electron impact (El) ionization gas chromatography/mass spectrometry (Cp Py-GC/MS) and pyrolysis-field ionization mass spectrometry (Py-FIMS). In contrast to the fragmenting El ionization, soft ionization methods, such as field ionization (FI) and field desorption (FD) each in combination with MS, result in the formation of molecule ions either without, or with only very low, fragmentation (Lehmann and Schulten, 1976 Schulten, 1987 Schulten and Leinweber, 1996 Schulten et al., 1998). The molecule ions are potentially similar to the original sample, which makes these methods particularly suitable to the investigation of complex environmental samples of unknown composition. 

CF4 is widely used as a feed gas for plasma etching in the microelectronic industry dissociative electron collisions ultimately determine the constituents in the fragmentation of the parent molecule, producing the neutral etch-active species F and heavier molecular fragments which may cause surface damage and contamination. The electron impact dissociative ionization of CF4 has therefore been investigated thoroughly71. 

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