Ionization by electron impact

We say the molecule AB has been ionized by electron impact The species that results called the molecular ion, is positively charged and has an odd number of electrons—it IS a cation radical The molecular ion has the same mass (less the negligible mass of a single electron) as the molecule from which it is formed... 

Section 13 22 Mass spectrometry exploits the information obtained when a molecule is ionized by electron impact and then dissociates to smaller fragments Pos itive ions are separated and detected according to their mass to charge (m/z) ratio By examining the fragments and by knowing how classes of molecules dissociate on electron impact one can deduce the structure of a compound Mass spectrometry is quite sensitive as little as 10 g of compound is sufficient for analysis... 

Ionization by electron impact has been shown (11) to occur at about 16.1 volts. Condon has given the explanation of the discrepancy between this and the band spectrum value in terms of... 

FIGURE 4.4 Schematic of threshold behavior of ionization processes. Under ideal conditions, one expects a step function for photoionization, a linear variation with energy under electron impact, and a parabolic dependence for double ionization by electron impact. 

The particle beam system is a simple transport device, very similar to a two-stage jet separator. The solvent vapour is pumped away, while the analyte particles are concentrated in a beam and allowed to enter the mass spectrometric source. Here they are vapourized and ionized by electron impact. 

Chemical Ionization (Cl) The vaporized sample is introduced into the mass spectrometer with an excess of a reagent gas (commonly methane) at a pressure of about 1 torr. The excess carrier gas is ionized by electron impact to the primary ions CH4,+ and CH3+. These react with the excess methane to give secondary ions. 

These Cl [M + H]+ ions (quasimolecular ions) are often prominent. Chemical ionization spectra sometimes have prominent [M — H]+ ions because of hydride ion abstraction from the M,+ ion by CH5+. Since the [M + H]+ ions are chemically produced, they do not have the great excess of energy associated with ionization by electron impact, and they undergo less fragmentation. For example, the El spectrum of 3,4-dimethox-yacetophenone shows, in addition to the molecular ion at m/z 180, 49 fragment peaks in the range of mJz 40-167 these include the base peak at m/z 165 and prominent peaks at m/z 137 and m/z 77. The CH4 induced Cl spectrum shows the quasimolecular ion (M + H+, m/z 181) as the base peak (100%), and virtually the only other peaks, each of just a few percent intensity, are the... 

The path of the laser beam and the detector (the ionizer in this case) define a plane perpendicular to the scattering plane in which the source of the molecular beam can be rotated to some scattering angle a. Neutral photofragments are detected through ionization by electron impact. Ions formed in this way can be mass selected in electric and/or magnetic fields. 

This instrument [7] measures three types of ions in a sequential mode the positive and negative ions emitted from the surface of the ion emitter, and the neutral species volatilizing from the surface and ionized by electron impact (El). A commercially available quadrupole mass spectrometer equipped with an El source was modified to allot a specially designed thermal emitter to be just barely inserted into the ionization chamber. The chamber is much cooler than the emitter there-... 

Mass-spectra of the gases eliminated from the specimens under elevated temperature were taken on mass-spectrometer MI-1201B (Sumy, USSR). The gas in ion source was ionized by electron impact (electron energy 70eV). Samples were placed in the quartz ampoule equipped by adjustable heater and connected through the needle valve with inlet system of mass-spectrometer. The sample was pumped out during one day up to the pressure 2xlO"5Pa to remove weakly bounded surface... 

K. Kiss, G. Kalman, J. Palinkas, B. Schlenk, Investigation of inner-shell ionization by electron impact in the 60-600 keV energy region, Acta Phys. Hung. 50 (1981) 97. 

Figure 1 The schematic representation of various electronic excitation mechanisms due to ac or dc external electric fields (a) the tuneling electrons from the valence band (VB) to the conduction band (CB) and ionization of an acceptor state (-o-) (Zener effect) followed by electron-hole recombination, indicated by horizontal and vertical arrows, respectively (b) excitation or ionization by electron impact (c) recombination of electrons ( ) and (o) holes at a semiconductor p-n junction and (d) bulk recombination of electrons and holes injected from electrodes. Adapted from Ref. 2...

We have performed data evaluation for hydrocarbons with the help of Prof. R. Janev. As a guest professor at NIFS, he worked on the data evaluation of charge exchange by proton impact and ionization by electron impact. They are published as NIFS DATA series [7,8], Dr. Y. Ralchenko and... 

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