ICR spectroscopy

Comisarow M B and Marshall A G 1996 Early development of Fourier transform ion cyclotron resonance (FT-ICR) spectroscopy J. Mass Spectrom. 31 581-5... 

When laser-ablated Ni atoms were reacted with CS2 during cocondensation in excess argon, the C-bonded Ni( /-CS2) and side-on bonded Ni(//2-CS)S complexes were formed on annealing, whereas the inserted SNiCS was formed on photolysis. All species were characterized by IR spectroscopy and DFT calculations.2466 The reaction of low-valent [Ni(CO)J (x=2, 3) with CS2 has been studied by FT-ICR spectroscopy.2467... 

Heilbronner and coworkers94 have studied several 2-, 3- and 4-substituted quinuclidines (23-25) by PES and ICR spectroscopy. A linear correlation of the gas-phase basicities and the ionization energies—relative to the unsubstituted parent molecule—was established. Comparison of the solution pKa values with gas-phase basicities revealed that 2-substituted quinuclidines (23) exhibit sizeable solvent-induced proximity effects, i.e. that the corresponding quinuclidinium ions are more acidic in solution than expected on the basis of proton affinities. 

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... 

Comisarow, M.B. Marshall, A.G. The Early Development of Fourier Transform Ion Cyclotron Resonance (FT-ICR) Spectroscopy. J. Mass Spectrom. 1996, 37,581-585. 

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]-... 

Application of pulsed ion gas-phase cyclotron resonance (ICR) spectroscopy to proton affinities of the derivatives 2-methoxypyridine and N- methylpyridin-2-one confirm previous deductions on the enthalpy of 2-hydroxypyridine-pyridin-2-one tautomerism (76JA6048), provided that the difference between the influences of O-methylation on 2-hydroxypyridine and A-me thy lat ion in pyridin-2-one are taken into account. These measurements have been further clarified and extended to other gas phase basicity measurements (79JA1361). A similar estimation of the gas phase basicities of 2- and 4-pyridinethiols and 2- and 4-pyridinethiones confirms that the thiol form is predominant in the gas phase (77TL1777), in line with previous studies involving mass spectrometric deuterium isotope studies (75BSB465). Photoelectron spectroscopy has also been employed in such studies (see Section 2.04.3.6 and Figure 21 for details) <77JCS(P2)1652>. 

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). 

Pulsed ICR spectroscopy was used to measure the IEs due to CD3 substitution on the proton-transfer equilibria of some methylbenzenes.95 Toluene-<73 is 0.33 kcalmol-1 less basic than toluene itself, consistent with the lower ability... 

Closely related to the omegatron mass spectrometer is the ion cyclotron resonance (ICR) mass spectrometer. Sommer and Thomas devised the ICR mass spectrometer by combining the techniques of nuclear magnetic resonance absorption and the basic omegatron. Wobschall, Graham and Malone and Henis have described the ICR spectrometer in detail and indicated its applications to the study of ion-molecule reactions and of negative ions. Baldeschwieler and Woodgate have reviewed ICR spectroscopy and included discussions of the... 

In this study, gaseous organic cations were generated by the technique of ion cyclotron resonance (ICR) spectroscopy, which is a form of mass spectroscopy... 

The pyrrole-like nature of the bridgehead nitrogen and pyridine-like nature of N-1 certainly suggest that reaction would be expected to occur at N-1. The first edition described UV data which indicated that N-1 was the site of protonation. Further experimental support for this has come from magnetic circular dichroism spectra <85JOC302>, and from the measurement of the proton affinity in the gas phase using ICR spectroscopy <88JA2699). 

One of the early successes of ion cyclotron resonance (ICR) spectroscopy was its application to obtaining accurate proton affinity information by measuring equilibrium constants for reaction 14 (48,49). The equilibrium constant K can be determined both from the steady state ratio of BHVaH, which becomes constant beyond some trapping time (the ratio of the neutrals A/B is known from the partial pressures and remains constant), and by measuring the forward... 

Another technique which has no parallel in conventional mass spectroscopy and thus underlines the usefulness of ICR spectroscopy is the double-resonance technique In most cases the yield of an ion-molecule reaction... 

Table 5. Thermal energy rate constants determined with ICR spectroscopy...

As in the application of Fourier methods to other spectroscopies, the application of Fourier methods to ICR spectroscopy permits the whole ICR spectrum to be obtained very quickly. For example, an FT-ICR spectrum is given below which extends from m = 50 to m = 1200 amu. That spectrum resulted from transient FT-ICR signals that were observed for only 1.6 sec. In contrast, a conventional ICR spectrometer would require about 30 min to scan up to m = 200 and would be unable to scan above that mass. 

One feature of FT-ICR spectroscopy which is particularly valuable for ion-molecule reaction studies is the double resonance experiment.16 In the ICR double resonance experiment, a reactant ion is ejected from the ICR cell as soon as it is formed. Product ions that result from that reactant ion are then absent from the spectra, and this absence can be used as a definitive diagnostic tool to identify ion-molecule reaction pathways. An attractive feature of the double resonance experiment when performed on FT-ICR spectrometers16 is that all product ions which are derived from a particular reactant ion are identified in a single double resonance experiment. Conventional ICR spectrometers require many double resonance experiments, one for each product ion, to discover the same information about the ion-molecule reaction system. Examples of double resonance experiments performed on an FT-ICR spectrometer are shown in Figure 8, taken from the ion-molecule study described below. Note that in Figure 8, eight different ions are simultaneously identified as ion-molecule reaction products that have the cyclopentadienylchromium ion as their chemical precursor. 

While the above work illustrates that the capability of the ICR technique for studying ion-molecule reactions is greatly enhanced by the use of Fourier techniques, it is possible that other applications of FT-ICR will also be important. One area where FT-ICR spectroscopy may be useful is analytical mass spectrometry.23,24 jhe slow speed and small mass range of conventional ICR spectrometers have been severe limitations to the use of ICR spectrometers for analytical mass spectrometry. These limitations are minimized by the application of Fourier methods and it is possible that FT-ICR spectroscopy may be a useful method for certain analytical mass spectrometric... 

Relative photodetachment cross sections have been measured in the wavelength range 725 to 1020 nm (1.71 to 1.22 eV) by ion cyclotron resonance (ICR) spectroscopy [1]. 

Reactions with neutral molecules have been investigated by the flowing afterglow (FA) technique (see [2, 3]) and earlier by ICR spectroscopy. The reaction usually starts with an initial nucleophilic attack of PHg on the neutral, followed by Intramolecular proton transfer and/or expulsion of a neutral fragment [4]. The table on p. 110 lists the rate constants k at 298 K (with an estimated error of 25% for the FA measurements [4]), efficiencies k/k oo (with kADo calculated by the average-dipole-orlentation theory of [5]), products (neutral products were not detected), and branching ratios, k and the branching ratio depend on the total pressure, when adducts are formed. Molecules, for which no reaction could be observed, are listed below the table. 

The equilibrium constants K of a large number of proton transfer reactions, some of them involving PH3, were determined by pulsed ICR spectroscopy, and a scale of the relative acidities of a series of acids in the gas phase at 298 K, 5ArG298, was deduced from the relation... 

Ketones. ICR spectroscopy of the ion-molecule reactions occurring in a PH3/CH3C(0)CH3 mixture was used among other techniques to evaluate the proton affinity of PH3 [23] see Section 1.3.1.5.2, p. 217. 

Fourier transform ion-cyclotron resonance mass spectrometry (FT-ICR-MS) is also an ion-trap technique. The concept of ICR spectroscopy was first described in 1930 by Lawrence and Edlefsen [55] and was later developed as a mass... 

The next step in both MAO-activated and MAO-free systems is believed to involve the transfer of an alkylide group to a Lewis acid (eqs. 8 and 9) or a proton (eq. 10), which creates an electron-deficient (14 e ) metal center with a site for the potential coordination of an olefin. The nature of the counterion strongly affects the abihty of the site to polymerize olefins, and indeed may change the active-site geometry enough to drastically change the selectivity of polymerization as well as the chain-transfer rate. Cation-anion interactions have been reviewed by Bochmann (125). The reactivity of anion-free cationic metallocenes has been probed by ion-cyclotron resonance (ICR) spectroscopy (126). 

Both ICR spectroscopy and Cl mass spectrometry can be used to measure the relative basicities of compounds by studying exchange reactions of the type... 

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