Charge-transfer chemical ionization

Rare gases, nitrogen, carbon monoxide and other gases with high ionization potential react by charge exchange  

A radical cation is obtained, as in El, but with a smaller energy content. Less fragmentation is thus observed. In practice, these gases are not used very often. 

Two examples of chemical ionization (isobutane) spectra. The top spectrum is that of a pure compound. The bottom spectrum is that of a mixture of two compounds with masses 261 and 270. They correspond respectively to the loss of hydrogen cyanide and water. 

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A third method for generating ions in mass spectrometers that has been used extensively in physical chemistry is chemical ionization (Cl) [2]. Chemical ionization can involve the transfer of an electron (charge transfer), proton (or otlier positively charged ion) or hydride anion (or other anion). 

Chemical ionization (Cl) The formation of new ionized species when gaseous molecules interact with ions. This process may involve the transfer of an electron, proton, or other charged species between the reactants in an ion-molecule reaction. Cl refers to positive ions, and negative Cl is used for negative ions. 

All electrochemical techniques measure charge transferred across an interface. Since charge is the measurable quantity, it is not surprising that electrochemical theory has been founded on an electrostatic basis, with chemical effects added as a perturbation. In the electrostatic limit ions are treated as fully charged species with some level of solvation. If we are to use UHV models to test theories of the double layer, we must be able to study in UHV the weakly-adsorbing systems where these ideal "electrostatic" ions could be present and where we would expect the effects of water to be most dominant. To this end, and to allow application of UHV spectroscopic methods to the pH effects which control so much of aqueous interfacial chemistry, we have studied the coadsorption of water and anhydrous HF on Pt(lll) in UHV (3). Surface spectroscopies have allowed us to follow the ionization of the acid and to determine the extent of solvation both in the layer adjacent to the metal and in subsequent layers. 

Optical charge transfer (CT) is commonly observed in un-symmetrical molecules or molecular complexes in which there are sites of distinctly different ionization energies and electron affinities. The origin and properties of optical charge transfer transitions provide the basis for this account. A convenient place to begin chemically is with mixed-valence compounds and two examples are shown below (1-3). In the first (eq 1), the sites of different oxidation states are held in close... 

MS involves the separation of ions based on their mass-to-charge ratio (m/z). The concept was invented a century ago1 with a dramatic impact on analytical chemistry.2-3 The fundamental principle of MS requires vaporization of the molecules in the gas phase and in ionization. Early ionization methods such as electron impact (El) and chemical ionization (Cl)4-5 were limited to small organic molecules that were volatile and stable to heat and amenable to transfer into high vacuum. Introduction of the fast-atom-bombardment (FAB) method of ionization6... 

Figure 14.3 Principle of atmospheric pressure chemical ionization. The dissolved analyte is sprayed through a capillary. Evaporation of the solvent is supported by a heated gas stream. Within the source, a plasma is formed by a Corona discharge needle, which creates the charged reagent gas (here HgO+j. The ionization of the analyte (M) is performed by the transfer of the charge (proton) via ion-molecule reactions.

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