Electron ionization schematic

Figure Bl.7.1. Schematic diagram of an electron ionization ion source source block (1) filament (2) trap electrode (3) repeller electrode (4) acceleration region (5) focusing lens (6).

Figure 2.2 Schematic view of the electron ionization source, a, Ion repeller h, anode c, acceleration and focalization plates N, S, magnet poles...

Figure 2.18 Schematic diagram showing the hypothetical behaviour of a molecule ionized by electron ionization (a) and its mass spectrum (b)...

Fig. 2.2. Electron ionization can be represented by a vertical line in this diagram. Thus, ions are formed in a vibrationaUy excited state if the intemuclear distance of the excited state is longer than in the ground state. Ions having internal energies below the dissociation energy D remain stable, whereas fragmentation will occur above. In few cases, ions are unstable, i.e., there is no minimum on their potential energy curve. The lower part schematically shows the distribution of Franck-Condon factors, fyc, for various transitions.

Fig. 5.3. Schematic time chart of possible electron ionization processes. Reprinted from Ref. [4] with permission. John Wiley Sons, 1986.

Figure 2.34 Schematic of an electron ionization source with Knudsen cell.

Two independent sets of ionization radii for all atoms have been calculated [53, 7] using exponential parameters p = 20 and 100, respectively. In both cases a clear periodic relationship appears, but the values at p = 100 are consistently lower. This observation reflects the steepness of the barrier that confines the valence electron, shown schematically in Figure 5.1. 

The mass spectrometric analysis starts with an ionization process (see also Section 3.5). This ionization takes place in the ion source of the MS instrument, where the analyte is introduced as gas phase. There are two common ionization procedures used for GC/MS electron ionization (El) and chemical Ionization (Cl). Other ionization procedures are also used in mass spectroscopy (see below and Section 5.4). The El process consists of an electron bombardment, which is commonly done with electrons having an energy of 70 eV. The electrons are usually generated by thermoionic effect from a heated filament and accelerated to the required energy. A schematic diagram of an El source is shown in Figure 5.3.1. 

At its simplest, mass spectrometry (MS) is a technique for measuring the mass, and therefore the molecular weight (MW), of a molecule. In addition, it s often possible to gain structural information about a molecule by measuring the masses of the fragments produced when molecules are broken apart. There are several different kinds of mass spectrometers available, but one of the most common is the electron-ionization, magnetic-sector instrument shown schematically in Figure 12.1 (p. 442). 

Figure 16.17 Electron ionization. The collision of an electron with a molecule m, creates a parent ion and fragment ions and in direct succession. The neutral fragments, and m 2 pass undetected. An illustration for the case of benzene is shown. Below, the schematic of an ionization chamber, also known as a collision chamber (or ion source). A magnetic field keeps the electron beam focused across the ion source and onto a trap by a spfraUing movement that enhances the efficiency of this electron gun.

A schematic of a particle beam interface is shown in Figure 21.13. The eluent from the HPLC column is nebulized using helium gas to form an aerosol in a reduced pressure chamber heated at 70°C. A cone with a small orifice is at the end of the chamber, which leads into a lower pressure area. The difference in pressure causes a supersonic expansion of the aerosol. The hehum and the solvent molecules are lighter than the analyte molecules and tend to diffuse out of the stream and are pumped away. The remaining stream passes through a second cone into a yet lower pressure area, and then the analyte vapor passes into the ion source. The particle beam interface produces electron ionization (El) spectra similar to those of GC-MS, so the vast knowledge of El spectra can be used for analyte identification. 

Figure 8.47 Schematic diagram of an electron ionization source. (From Watson, J.T. Introduction to Mass Spectrometry, 3rd ed. Lippincott-Raven Publishers Philadelphia, 1997, p. 140.)...

Schematic diagram of an electron ionization mass spectrometer (EI-MS).

Figure 15.3. Schematic of electron ionization (El) mass spectrometry.

Fig. 4.7 Schematic diagram of an electron ionization (or electron impact, El) mass spectrometer. During operation, the interior of the instrument is evacuated.

The ionization by light at 347.1 nm (3.57 eV energy) of phenothiazine incorporated in NaLS micelles in water has been attributed to the rapid tunnelling of an electron from excited phenothiazine through the double layer into unoccupied electronic redox levels of the system aq/cj [57]. This photoionization is promoted by co-solubilization of duroquinone which prevents ejection of electrons from the phenothiazine into the water phase. It is suggested [57] that the phenothiazine/water/quinone/micelle system offers a simple model for electron transfer in photosynthetic systems and for the heterogeneous catalysis of the photodecomposition of water via the freed electrons. A schematic representation of the processes when the surfactant is anionic [58] is shown in Fig. 11.10. 

A schematic view of the GC-SIOMS apparatus is shown in Figure 2. The design of the SI probe assembly is such that the Re ribbon filament (for instance, 6 X 0.75 X 0.025 mm) can be placed in the center of the conventional electron ionization (El) ion source chamber. This combined ion source allows an easily inter-... 

Flame Ionization Detector Combustion of an organic compound in an Hz/air flame results in a flame rich in electrons and ions. If a potential of approximately 300 V is applied across the flame, a small current of roughly 10 -10 A develops. When amplified, this current provides a useful analytical signal. This is the basis of the popular flame ionization detector (FID), a schematic of which is shown in Figure 12.22. 

Schematic diagram showing the development of a dipolar field and ionization on the surface of a metal filament, (a) As a neutral atom or molecule approaches the surface of the metal, the negative electrons and positive nuclei of the neutral and metal attract each other, causing dipoles to be set up in each, (b) When the neutral particle reaches the surface, it is attracted there by the dipolar field with an energy Q,. (c) If the values of 1 and <() are opposite, an electron can leave the neutral completely and produce an ion on the surface, and the heat of adsorption becomes Q,. Similarly, an ion alighting on the surface can produce a neutral, depending on the values of I and <(), On a hot filament the relative numbers of ions and neutrals that desorb are given by Equation 7.1,which includes the difference, I - <(), and the temperature, T,...

Schematic diagram of a flame ionization detector. Ions and electrons formed in the flame provide an electrically conducting path between the flame at earth potential and an insulated cylindrical metal electrode at high potential. surrounding the flame the flow of current is monitored, amplified, and passed to the recording system.

Figure 1 Schematic of DC glow-discharge atomization and ionization processes. The sample is the cathode for a DC discharge in 1 Torr Ar. Ions accelerated across the cathode dark space onto the sample sputter surface atoms into the plasma (a). Atoms are ionized in collisions with metastable plasma atoms and with energetic plasma electrons. Atoms sputtered from the sample (cathode) diffuse through the plasma (b). Atoms ionized in the region of the cell exit aperture and passing through are taken into the mass spectrometer for analysis. The largest fraction condenses on the discharge cell (anode) wall.

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