Fragmentation phenomenon description

Figure 6.4. Fragmentation spectrum of a tryptic peptide obtained from bovine serum albumin. Peptide sequence LGEYGFQNALIVR, monoisotopic [M + H]+ = 1479.796, monoisotopic [M+2H]2+ =740.402. Upper panel full scan MS spectrum. Lower panel MS/MS spectrum of a doubly-charged ion at 740.7 m/z with a ladder of y ions, the distances between which correspond to amino acid residues (upper row of letters). A shorter series of b ions is also seen (lower row of letters). See Fig. 6.5 for description of nomenclature. Note the often observed phenomenon where multiply-charged ions lose the charge during fragmentation process and, therefore, have higher m/z values than the original parent ion.

In terms of atomistic description of the phenomenon of catalysis, the border between these two approaches is determined by the rate of attenuation of the electron perturbation in a solid with the distance from an adsorbed molecule as well as by the degree of similarity between electron structures of the whole surface of a solid and of a fragment considered as a model of the adsorption or of an active site. For a long time this problem lacked an unambiguous solution. Therefore both approaches were equally widely used to describe catalytic phenomena, often without proper regard to specific features of the systems considered. Thus, active sites on metal catalyst surfaces were frequently modeled by individual metal atoms. On the contrary, catalysis on insulator oxide surfaces was sometimes discussed in terms of their cooperative electron properties. 

As indicated by this brief description, the process of adsorption of atoms and molecules on solid surfaces involves kinetic as well as static aspects. Obviously, the sequence of steps (l)-(5) above is a complex kinetic phenomenon. On the other hand, measuring the physical properties of an adsoibed atom, molecule or fragment concerns the static nature of that species. In both cases the structure and chemical composition of the clean surface is of importance, because the properties of the adsoibed species depend sensitively on the local structure and chemistry of the adsorprion site. Thus the description of adsorbed layers on surfaces is not thinkable without a detailed knowledge of clean surfaces. It is therefore no coincidence that the current volume of Adsorbed Layers follows the Landolt-Bomstein volume on Clean Surfaces. Important data characterizing clean surfaces of metals, semiconductors etc. are collected in the Landolt-Bomstein volumes III/24, subvolumes A-D. 

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