Ion electron reactions

Thus in one of these two oxidation-reduction reactions the bromine-bromide ion electron reaction proceeds in one direction, and in the other reaction it proceeds in the other direction. 

Silivra, OA., Ivonin, I.A., Kjeldsen, F., and Zubarev, RA. (2004) Ion-electron reactions in a quadrupole ion trap Realization, first results and prospects. Proceedings, 52nd Annual Conference of the American Society for Mass Spectrometry, Nashville, TN. 

Figure 4 The ion chemistry of the upper terrestrial atmosphere. Only biomolecular ion-neutral reactions occur, and ion-electron reactions (dissociative recombination) maintain the ionization equilibrium.

A final category of gas-phase ion-electron reactions as activation methods for tandem mass spectrometry involves interactions between singly charged precursor ions and free electrons (note that ECD, hot ECD, ETD, and EDD require at least doubly charged precursor ions). The first reaction of this type, involving singly protonated peptides, was reported by Zubarev... 

Yang, J. Hakansson, K. Fragmentation of oligoribonucleotides from gas-phase ion-electron reactions. J. Am. Soc. Mass Spectrom. 2006,17, 1369-1375. 

Kieinnijenhuis, A. J. Kjeldsen, E Kallipoutis, B. Haselmann, K. E Jensen, O. N. Analysis of histidine phosphorylation using tandem MS and ion-electron reactions. Anal. Chem. 2007, 7450-7456. 

Kebarle P 1988 Pulsed electron high pressure mass spectrometer Techniques for the Study of Ion-Molecule Reactions ed J M Farrar and W FI Saunders (New York Wiley-Interscience)... 

The one-electron reduction of thiazole in aqueous solution has been studied by the technique of pulse radiolysis and kinetic absorption spectrophotometry (514). The acetone ketyl radical (CH ljCOH and the solvated electron e were used as one-electron reducing agents. The reaction rate constant of with thiazole determined at pH 8.0 is fe = 2.1 X 10 mole sec in agreement with 2.5 x 10 mole sec" , the value given by the National Bureau of Standards (513). It is considerably higher than that for thiophene (6.5 x 10" mole" sec" ) (513) and pyrrole (6.0 X10 mole sec ) (513). The reaction rate constant of acetone ketyl radical with thiazolium ion determined at pH 0.8 is lc = 6.2=10 mole sec" . Relatively strong transient absorption spectra are observed from these one-electron reactions they show (nm) and e... 

Ionizing collision. An ion/neutral reaction in which an electron or electrons are stripped from the ion and/or the neutral species in the collision. Generally, this term describes collisions of fast-moving ions or atoms with a neutral species in which the neutral species is ionized. Care should be taken to emphasize if charge stripping of the ion has taken place. 

Unlike traditional surface science techniques (e.g., XPS, AES, and SIMS), EXAFS experiments do not routinely require ultrahigh vacuum equipment or electron- and ion-beam sources. Ultrahigh vacuum treatments and particle bombardment may alter the properties of the material under investigation. This is particularly important for accurate valence state determinations of transition metal elements that are susceptible to electron- and ion-beam reactions. Nevertheless, it is always more convenient to conduct experiments in one s own laboratory than at a Synchrotron radiation focility, which is therefore a significant drawback to the EXAFS technique. These focilities seldom provide timely access to beam lines for experimentation of a proprietary nature, and the logistical problems can be overwhelming. 

Despite this, they are good solvents for chloride-ion transfer reactions, and solvo-acid-solvo-base reactions (p. 827) can be followed conductimetri-cally, voltametrically or by use of coloured indicators. As expected from their constitution, the trihalides of As and Sb are only feeble electron-pair donors (p. 198) but they have marked acceptor properties, particularly towards halide ions (p. 564) and amines. 

Addition of methane to the ion source at a pressure of about 0.5 Torr causes almost all of the electrons entering the ion source to collide with methane molecules. The first event is the expected production of a molecular ion (eq. 3). The molecular ion can then undergo fragmentation (eq. 4) or because of the high pressure of neutral methane, ion-molecule reactions can occur (eqs. 5 and 6). 

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. 

It was mentioned earlier (Sec. 8.6) that for iodo-de-diazoniation no catalyst is necessary because the redox potential of the iodide ion (E° = 1.3 V) is sufficient for an electron transfer to the arenediazonium ion. The reaction was actually observed by Griess (1864 c). Four iodo-de-diazoniation procedures are described in Organic Syntheses. For the syntheses of iodobenzene and 4-iodophenol (Lucas and Kennedy, 1943, and Daines and Eberly, 1943, respectively) KI is used in equimolar quantity and in 1.2 molar excess. However, for 2-bromoiodobenzene and for 1,3,4-triiodo-5-nitrobenzene (replacement of a diazonio group in the 4-position by iodine), up to... 

Intercalation chemistry electron/ion transfer reactions. R. Schollhom, Comments Inorg. Chem.,... 

Method (b) corresponds to the usual method of investigating ion-molecule reactions in a high pressure mass spectrometer although charge exchange with slow ions is used instead of electron impact. After preliminary work (9, 23), the method was fully developed by Szabo 20, 21, 22). 

Some of the problems encountered in the mass spectrometric study of ion-molecule reactions are illustrated in a review of the H2-He system (25). If the spectrometer ion source is used as a reaction chamber, a mixture of H2 and He are subjected to electron impact ionization, and both H2+ and He+ are potential reactant ions. The initial problem is iden-... 

Reactions of Complex Ions. For reactions of systems containing H2 or HD the failure to observe an E 1/2 dependence of reaction cross-section was probably the result of the failure to include all products of ion-molecule reaction in the calculation of the experimental cross-sections. For reactions of complex molecule ions where electron impact ionization probably produces a distribution of vibrationally excited states, kinetic energy transfer can readily open channels which yield products obscured by primary ionization processes. In such cases an E n dependence of cross-section may be determined frequently n = 1 has been found. 

Since the observation made in study of the formation HeH+ indicated that this product was not formed by reaction of He + with H2, it had been assumed that the exothermic heat of reaction of He+ ions with H2 is probably deposited in the product HeH + as internal energy, decomposing the product into H+ and He. This idea was cited by Light (16) in his phase space theory of ion-molecule reactions to account for the failure to observe HeH+ from reactions with He+ ions. The experimental difficulty in the mass spectrometric investigation of this process is that H + formed by electron impact tends to obscure the ion-molecule-produced H+ so that a sensitive quantitative cross-section measurement is difficult. 

In 1960 Tal roze and Frankevich (39) first described a pulsed mode of operation of an internal ionization source which permits the study of ion-molecule reactions at energies approaching thermal energies. In this technique a short pulse of electrons is admitted to a field-free ion source to produce the reactant ions by electron impact. A known and variable time later, a second voltage pulse is applied to withdraw the ions from the ion source for mass analysis. In the interval between the two pulses the ions react under essentially thermal conditions, and from variation of the relevant ion currents with the reaction time the thermal rate constants can be estimated. 

In brief, the method consists of introducing small amounts (partial pressures of 10 3-10 4 torr) of the substance to be investigated into the ionization chamber of a mass spectrometer which contains a high pressure (1 torr) of methane, the reactant gas. Ionization is effected by electron impact, and because the methane is present in such an overwhelming preponderance, all but a negligibly small amount of the initial ionization occurs in the methane. The methane ions then undergo ion-molecule reactions to produce a set of ions which serve as reactant ions in the chemical ionization process. The important reactant ions formed from... 

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