PIPECO and charge exchange

Since the special PIPECO and charge exchange techniques permit determination of rate coefficients k(E) (Sects. 3.2.1, 3.3.2 and 3.4.1), it should be possible to determine kinetic isotope effects. 

There is one obvious difficulty in determining intramolecular kinetic isotope effects with the present PIPECO techniques for metastable ions (Sect. 3.2.1), which is that peaks for product ions from isotopically labelled molecules will overlap. Indeed, peaks for ions separated by only one mass unit will typically be largely superimposed. The time-of-flight technique is, in effect, measuring velocity and what is required is measurement of mass and translational energy in separate analysers. The problem 

Charge exchange will suffer the same problems with intramolecular kinetic isotope effects as PIPECO if single-focussing mass spectrometers are used. Charge exchange with a double-focussing mass spectrometer should, however, allow determinations of intramolecular kinetic isotope effects. 

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In these rather special PIPECO experiments, ions are being produced with selected internal energy and their lifetimes are measured. FIK achieves measurement of time, and PIPECO in its usual form and charge exchange fix energy. To both preselect energy and measure time is the desired, yet rare, level of experiment in mass spectrometry. 

Charge exchange and collisional activation of energy-selected ions have been studied by PIPECO [21, 783]. 

If metastable ions are observed in charge exchange experiments, both the lifetime and the internal energy of the reactant are defined as in the analogous PIPECO experiment. The energy at which the intensities of the reactant and fragment ion in the breakdown curve become comparable may be used as a guide as to where to look for metastable ions,... 

Benzene has been investigated rather thoroughly by PIPECO [269, 277, 278, 758, see also 715] however, its unimolecular ion chemistry remains somewhat enigmatic. It was suggested, on the basis of charge exchange results, that the decompositions of the molecular ion to form (CaHa)" and (04114) did not compete with those forming and... 

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