Ion Cyclotron Resonance ICR

Equation (5.7) describes the radius r of the ions orbits (B is the magnetic field strength, v the velocity of the ions on the circuit)  

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The most widely used type of trap for the study of ion-molecule reactivity is the ion-cyclotron-resonance (ICR) [99] mass spectrometer and its successor, the Fourier-transfomi mass spectrometer (FTMS) [100, 101]. Figure A3.5.8 shows the cubic trapping cell used in many FTMS instmments [101]. Ions are created in or injected into a cubic cell in a vacuum of 10 Pa or lower. A magnetic field, B, confines the motion in the x-y... 

Other types of mass spectrometer can use point, array, or both types of ion detection. Ion trap mass spectrometers can detect ions sequentially or simultaneously and in some cases, as with ion cyclotron resonance (ICR), may not use a formal electron multiplier type of ion collector at all the ions can be detected by their different electric field frequencies in flight. 

Ion cyclotron resonance (ICR) analyzer A device to determine the mass-to-charge of an ion in a magnetic field by measuring its cyclotron frequency. 

In obtaining experimental information about the isomeric forms of ions, a variety of techniques have been used. These include ion cyclotron resonance (ICR),31 flow tube techniques, notably the selected ion flow tube (SIFT),32 and the selected ion flow drift tube (SIFDT)32 (and its simpler variant33), collision induced dissociation (CID),10,11 and the decomposition of metastable ions in mass spectrometers.13 All of these techniques are mentioned in the text of Section in whore they have provided data relevant to the present review. 

In the ion cyclotron resonance (ICR) analyzer, ions are trapped by a strong magnetic field. The magnetic field will cause the ions to move in a circular motion with a frequency that depends on their m/z.. Ions to be detected are excited to make them move closer to the detection plates. Then a small current will be induced in the plate each time an ion passes by. Since the ions with different m/z have different ICR frequencies, each generated current frequency will correspond to a certain m/z value. 

Principle. The principle of the ion cyclotron resonance was developed in the early 1930s by Lawrence and coworkers [252, 253]. The utilization of the ion cyclotron resonance (ICR) technique for mass spectrometry was introduced around 1950 by Sommer et al. [254, 255], and combination with the Fourier transform (FT) technique was developed by Comisarow and Marshall in 1974 [256], Coupling of external sources to an FTICR analyzer was first done in 1985 [257, 258],... 

In the ion cyclotron resonance (ICR) cell CID is performed by resonant excitation of the precursor ion and subsequent collisions with the background gas. One serious drawback with on-resonance excitation in the ICR cell is that the risk for ion losses due to... 

The major activity in gas-phase studies now depends on the use of modem techniques such as ion cyclotron resonance (ICR). Thus, as already mentioned (Section ELD). Fujio, Mclver and Taft131 measured the gas-phase acidities, relative to phenol, of 38 meta- or para-substituted phenols by the ICR equilibrium constant method, and their results for +R substituents led them to suggest that such substituents in aqueous solution exerted solvation-assisted resonance effects. It was later163 shown by comparison of gas-phase acidities of phenols with acidities of phenols in solution in DMSO that solvation-assisted resonance effects could also occur even when the solvent did not have hydrogen-bond donor properties. Indeed for p-NC>2 and certain other substituents these effects appeared to be larger than in aqueous solution. 

The advent of techniques that enable the study of fast reactions in the gas phase, such as ion cyclotron resonance (ICR) spectrometry, Fourier-transform ion cyclotron resonance spectrometry (FT-ICR) and high pressure mass spectrometry (HPMS), allowed the measurement of the gas-phase proton affinities for strong bases84-86 as well as for... 

A variety of studies on nucleophilic displacement reactions have been carried out in the gas phase, utilizing pulsed ion cyclotron resonance (ICR) spectroscopy. Many of these reactions occur with conveniently measurable efficiencies... 

Rate Measurement. We have used pulsed ion cyclotron resonance (ICR) spectroscopy to study these gas-phase, ion-molecule reactions. The method has been described elsewhere in considerable detail (5). Basically, ions are generated by pulsed electron impact and held in a magnetic-electric field trap for times up to about 1 sec, during which they can react with a... 

Ion cyclotron resonance ICR Trapped ions separation by cyclotron frequency (Lorentz force) in magnetic field... 

In order to perform two consecutive mass-analyzing steps, two mass analyzers may be mounted in tandem. This technique is applied with beam transmitting devices, i.e., TOF, sector and quadrupole analyzers can be combined that way tandem-in-space, Fig. 4.15). Alternatively, a suitable mass analyzer may be operated by combining selection, activation, and analysis in the very same place. Quad-mpole ion trap (QIT) and ion cyclotron resonance (ICR) instruments can perform such tandem-in-time experiments. 

Ion cyclotron resonance (ICR) spectroscopy has been used to determine the reaction enthalphy (A//r) of hydride-transfer reaction of silanes with various hydrocarbons having known hydride affinities (Reaction 2.19). The hydride affinities of R3Si+, D//(X3Si+—H ) = Affbase, were obtained from Equation (2.20) and are summarized in Table 2.6 [30,31]-... 

To overcome this, instrumental techniques such as pulsed high-pressure mass spectrometry (PHPMS), the flowing afterglow (FA) and allied techniques like the selected-ion flow tube (SIFT), and ion cyclotron resonance (ICR) spectrometry and its modem variant, Fourier transform mass spectrometry (FTMS), have been developed. These extend either the reaction time (ICR) or the concentration of species (PHPMS, FA), so that bimolecular chemistry occurs. The difference in the effect of increasing the pressure versus increasing the time, in order to achieve bimolecular reactivity, results in some variation in the chemistry observed with the techniques, and these will be addressed in this review as needed. 

Another important series of experiments has shown, by ion-cyclotron-resonance (ICR) studies, that monocyclic carbon rings can coalesce very efficiently to fullerenes (Scheme 1.9) [139]. The carbon rings are obtained by laser desorption of carbon oxide C (CO) p precursors, out of which, upon loss of CO, the cyclo[n]carbons Cjg,... 

Ion cyclotron resonance (ICR) gas phase hydroxy 76JA6048 79JA1361... 

Operation of the ion cyclotron resonance (ICR) spectrometer under equilibrium conditions allows the determination of K2 for the equilibrium in... 

Figure 16.8—Ion cyclotron resonance (ICR) mass spectrometer. Ion trajectories in the ICR cell are shown. Plates 5 and 6 are used for excitation, plates 3 and 4 are used to trap ions and plates 1 and l are used as the detection system. Ions can be formed inside or outside the ICR cell. Exampleofthe tg resouion a can be obtained with this type of spectrometer (R = 3 x I06), cf. 16.8.3.

The gas-phase heats of formation obtained from pulsed ion cyclotron resonance (ICR) spectroscopy showed that the tertiary 1-cyclopropyl-1-methylethyl cation (20) is more stable than the 1-phenyl-1-methylethyl cation by 0.8 kcalmol 1, while the secondary 1-cyclo-propylethyl cation (18) is less stable than the 1 -phenylethyl cation by 4.8 kcal moT125. Thus a substantial reversal of the stabilization of the phenyl over cyclopropyl groups is observed. The results were also rationalized by STO-3G calculations for the isodesmic reaction involving proton transfer (equation 71). 

Ion Cyclotron resonance (ICR) elec iron-impact ionization Photoiomzation-mass spectrometry... 

Figure 8. Schematic diagram of typical ion-cyclotron resonance (ICR) cell used for ion-molecule reaction studies. Regions A, B, and C designate ion source, analyzer, and ion collector regions, respectively. Electrodes 2 and 4 are used to apply trapping potential, 1 and 3 for source drift potential, 5 and 6 for analyzer drift and RF fields, and 7 to 10 for total ion collection.148...

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