Electron impact fragment generation

With the surface ionization source it is generally assumed that the reactant ion internal state distribution is characterized by the source temperature and that the majority of the reactant ions are in their ground electronic state. This contrasts with the uncertainty in reactant state distributions when transition metal ions are generated by electron impact fragmentation of volatile organometallic precursors (10) or by laser evaporation and ionization of solid metal targets (11). Many examples... 

Some simplification of the previously described picture results from the fact that the fragmentation due to the ionization procedure in a mass spectrometer (such as the electron impact) may generate similar fragments as pyrolysis (see Section 3.5). Therefore some of the ions seen in the mass spectrometer are generated either by pyrolysis and not fragmented in the mass spectrometer (seen as molecular ions) or by the fragmentation of larger molecules due to the ionization alone. Schematically the process can be described as follows ... 

The advantages of PMS over PGC for generating information about polymeric materials are its speed, sensitivity, ease of producing data that can be processed by a computer, and the elimination of the variables associated with GC. A major disadvantage of PMS is that a complex mixture is produced by a combination of pyrolysis and electron impact fragmentation, which makes a mass pyrogram more difficult to interpret than the chromatogram produced in PGC, in which only a pyrolytic breakdown is involved. 

Electron impact ionisation (El) stands for extensive fragmentation, but also produces molecular ions. The other ionisation methods shown in Table 6.10 mainly generate quasi-molecular ions for various compound classes. Protonation of organic compounds is one of the most fundamental processes of Cl, FAB and ESI mass spectrometry. Apart from electrospray (ESI), which... 

A potential source for generating monomeric 23 is found in the l,2Xs-oxa-phosphetanes 21 and 22 18-20>, Their mass spectra contain peaks at M+ — 140, corresponding to [2 + 2]-cycloreversion to olefin and 23 however, the latter fragment (m/e = 140) was not found in the mass spectra. Although it cannot be explicitly stated whether this fragmentation is induced by electron-impact or thermally, a thermal reaction in the mass spectrometer certainly appears plausible. Such a reaction can indeed be accomplished on a preparative scale under milder conditions, as previously reported for 21 (R = C6HS) (Sect. 2.1). 

Alternatively, the primary photofragments of Ib CO)] are probed by electron impact ionization of fragments formed on photolysis (33). Excitation into the same near UV band leads to generation of Mn(CO), Mi CCO) and M tCO). This experiment was also performed by excitation at 250 nm and 193 nm, of two higher electronic states of the molecule. 

An electron impact (El) ion source uses an electron beam, usually generated from a rhenium filament, to ionize gas-phase atoms or molecules. Electrons from the beam (usually 70 eV) knock an electron from a bond of the atoms or molecules creating fragments and molecular ions [366,534,535]. Several factors contribute to the popularity of El ionization in environmental analyses such as stability, ease of operation, simple construction, precise beam intensity control, relatively high efficiency of ionization, and narrow kinetic energy spread of the ions formed. 

Cooks, R.G. Williams, D.H. The Relative Rates of Fragmentation of Berrzoyl Ions Generated Upon Electron Impact from Different Precursors. Chem. Common. 1968, 627-629. 

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