Spectroscopy FT-ICR

The intrinsic basicity (i.e. the standard Gibbs energy change for reaction 158 in the gas phase) for a variety of compounds XC(=S)Y have been determined by means of Fourier Transform Ion Cyclotron Resonance Spectroscopy (FT ICR) by the groups of Abboud39 and of Gal520. 

Gas-phase transfers of hydride from methoxide to C02, CS2 and S02 have been observed by the flowing afterglow technique (Bierbaum et al., 1984) and by Fourier transform ion cyclotron resonance spectroscopy (FT-ICR) (Sheldon et al., 1985). With aldehydes and ketones, the normal gas-phase reaction with methoxide is enolate formation, but FT-ICR methods have been used to demonstrate reduction of non-enolizable aldehydes including benzaldehyde, pivalaldehyde, and 1-adamantylaldehyde. 

Several methods exist that allow the determination of the standard enthalpies of formation of the ionic species. The reader is referred to two recent rigorous and detailed chapters by Lias and Bartmess and Ervin. The vast majority of the experimental data reported here are obtained by means of Fourier transform ion cyclotron resonance spectroscopy (FT ICR), high-pressure mass spectrometry (HPMS), selected ion flow tube (SIFT), and pulsed-field ionization (PFI) techniques, particularly pulsed-field ionization photoelectron photoion coincidence (PFI-PEPICO). All these experimental techniques have been examined quite recently, respectively, by Marshall, Kebarle, B6hme," ° Ng" and Baer. These chapters appear in a single (remarkable) issue of the International Journal of Mass Spectrometry. An excellent independent discussion of the thermochemical data of ions, with a careful survey of these and other experimental methods, is given in Ref. 37. 

Fourier Transform Ion Cyclotron Resonance Spectroscopy FT-ICR DOUBLE RESONANCE... 

Van der Hage and co-workers [147] combined MALDI and Fourier-transform ion cyclotron mass spectroscopy (FT-ICR-MS) for the characterisation of polyoxyalkyleneamines. MALDI FT-ICR-MS was used to resolve intact, sodium ion cationised oligomer ions in the mass range from miz 500 to 3500. NMR was used to measure the average end-group distribution to provide insight into conformational differences. In this respect, FT-ICR-MS and NMR data were complementary. Combined results yielded detailed information about chemical composition distributions of polyalkyleneamines that hitherto it was not possible to obtain with either technique separately. Merits and limitations of the data produced with MALDI-FT-ICR-MS are discussed and compared with those of H- and C-NMR data [147]. 

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... 

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. 

Attempts have been made to observe and experimentally determine the structure of CH5+ in the gas phase and study it in the condensed state using IR spectroscopy,764 765 pulse electron-beam mass spectrometry,766 and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS).767 However, an unambiguous structure determination was unsuccessful. Retardation of the degenerate rearrangement was achieved by trapping the ion in clusters with H2, CH4, Ar, or N2. 

Identification of fulleranes by Raman spectroscopy and XRD is difficult due to complexity of obtained mixture. Precise determination of composition for white colored fullerane samples was performed using APPI FT-ICR mass spectrometry. 

This volume contains excellent discussions of the various methods for studying ion-molecule reactions in the gas phase, including high pressure mass spectrometry, ion cyclotron resonance spectroscopy (and FT-ICR) and selected ion flow tube mass spectrometry. 

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... 

The past decade has seen an explosion in investigations of molecular ions using a variety of optical spectroscopic techniques in conjunction with trapping mass spectrometers. The mass selection and ion storage capabilities of instruments such as 3-D QITs and FT-ICR mass spectrometers provide valuable control over the ion population under investigation. Moreover, thanks to modem ion sources, the size of molecules is no longer a limitation for gas-phase ion spectroscopic studies. A number of spectroscopic techniques have been developed to probe gas-phase molecules that will be fruitful when applied to the spectroscopy of trapped ions. 

In a series of studies Bickelhaupt et al. [64, 87, 88] investigated base-induced elimination reactions experimentally with Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectroscopy and theoretically with DF calculations. They applied the computational scheme of Baerends et al. [5], using the gradient corrections of Becke [89] for the exchange potential. They studied the fundamental class of reactions... 

The introduction of an >-substituent (CN, Cl, or OH) into a primary n-alkyl chloride considerably enhances the rate of 5 n2 chloride exchange in the gas phase. Reactivity trends suggest that the acceleration is due primarily to through-space solvation of the transition state, especially charge-dipole interactions. Potential-energy surfaces are discussed. In further work by the same group, the translational energy dependence of the rate constants of several gas-phase 5 n2 and carbonyl addition-elimination reactions has been measured by FT-ICR spectroscopy. The results were interpreted by RRKM calculations. 

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