Fourier Transform Ion Cyclotron Resonance Spectroscopy

Department of Chemistry University of British Columbia Vancouver, B.C. V6T 1Y6 CANADA 

This chapter discusses the principles of Fourier transform spectroscopy as applied to a type of mass spectrometry called ion cyclotron resonance (ICR) spectroscopy. 

As in any mass spectrometer, the ICR spectrometer has provision for ionizing a gaseous sample and then determining the masses of the ions that are formed. The ICR experiment is typically conducted at very low pressures, usually in the range 10 8 to 10 torr. The operating features of ICR spectrometers have been extensively re-viewedl and will be discussed only briefly here. 

According to Equation 1, an ensemble of ions of differing masses will have a spectrum of cyclotron frequencies which is characteristic of that ensemble. For a magnetic field strength of 1 tesla and a mass range of 15 amu to 1500 amu, the cyclotron frequency spectrun (Equation 1) extends from 10 kHz to 1 MHz and thus falls in the radiofrequency region of the electromagnetic spectrum. 

Once excited cyclotron motion has been achieved, the excited cyclotron motion at a particular ion mass will induce an alternating 

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Asamoto, B. and Dunbar, R.C., Analytical Applications of Fourier Transform Ion Cyclotron Resonance Spectroscopy, VCH, New York, 1991. 

M. B. Comisarow and A. G. Marshall. Fourier Transform Ion Cyclotron Resonance Spectroscopy. Chem. Phys. Lett., 25(1974) 282- 283. 

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. 

Comisarow, M.B. and Marshall, A.G. (1974) Fourier transform ion cyclotron resonance spectroscopy. Chem. Phys. Lett., 25, 282-3. 

When this chapter was in press, Beauchamp and coworkers reopened the discussion on the relative stabilities of silaethylene (40) and methylsilylene (45)377. They found, using Fourier transform ion cyclotron resonance spectroscopy, that silaethylene (40) is by 10 3 kcalmol"1 more stable than the isomeric methylsilyene 45. The experiments were corroborated by ab initio GVB-CI calculations which found that 40 is more stable than 45 by 11.6 kcal mol-1. The discrepancy between these recent results377 and the previous high level MO calculations, which predict a 40-45 energy difference of nearly zero (see Table 19), is puzzling. Further calculations and experiments are required to resolve this problem. 

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... 

Cr, Mo and W - The gas-phase ion chemistry of the chromium cycloheptatriene complexes [Cr(T -C7H8)(CO)3] was studied272 by Fourier Transform Ion Cyclotron Resonance Spectroscopy. The presence of a fragment ion [C5H6Cr]+ with the hydrido-ri -cyclopentadienyl structure was detected. Reaction of the same complex [Cr(Ti -C7H8)(CO)3] with the carbene complex [Cr(CO)5(=C(OMe)Me)] afforded273 an isomeric mixture of bicyclo[4.2.1]nonanone products. 

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