Gaussian metastable peaks

As stated above, the majority of metastable peaks have a Gaussian-type profile (Figure 2A). Indeed many peaks can be described by a simple variant of the Gaussian formula, h = exp(-at ) (where h is the fraction of the peak height at which the width, is... 

Figure 2 Simple Gaussian (A) and dished (B) metastable peaks. For comparison a typical profile for an undissociating ion beam is shown between them.

It is believed that the great majority of Gaussian-type metastable peaks arise from ion fragmentations with no reverse energy barrier, (Figure 3),... 

Figure 3 Potential energy profiles for ion fragmentations giving rise to Gaussian and flat-topped metastable peaks.

Fig. 2.14. Influence of the reverse activation energy on KER and thus, on peak shapes in metastable ion decompositions, suitable experimental setup as prerequisite. From left no or small reverse barrier causes Gaussian peak shape, whereas medium or yields flat-topped peaks and large For causes dish-shaped peaks.

FIGURE 9. CAD mass spectra of the CsHsO cations generated by (a) protonation of propynal and (b) dissociative El of methyl vinyl ketone. The accepted structures of these C3H3O+ cations are (a) HC=C—CH=OH+ (20+) and (b) H2C=CH—C=0+ (21+), respectively. Metastable 20+ loses approximately equal amounts of CO (Tq.s = 6.3 kimoF ) and C2H2 (T0.5 = 5.3 kJmoF ) whereas metastable 21+ only cleaves CO (To.5 = 0.45 kJmoF ) all peak shapes are gaussian. Adapted from Reference 50... 

In a magnetic sector instrument the signals of metastable ions appear as broad, mostly gaussian peaks in normal mass spectra. The location m may be calculated from the precursor ion mass nip and the product ion mass nia using the relation ... 

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