Fragmentation ionic

Versa V, Campagnoia P J, Nandi S, Larsson M and Lineberger W C 1996 Protofragements of ir-Ar ciusters observation of metastabie isomeric ionic fragments J. Ghem. Phys. 105 2298-308... 

Fragment ion. An electrically charged dissociation product of an ionic fragmentation. Such an ion may dissociate further to form other electrically charged molecular or atomic moieties of successively lower formula weight. 

The backbone bonds are polar but the structure is balanced and the polymer is quite a good dielectric. Reported data on resistivity indicate only moderate values presumably because of ionic fragments, impurities and additives. 

The experimental approaches described above are examples of relative methods, wherein a thermochemical property is measured with respect to that of a standard, or an anchor. The quality of these measurements ultimately depends on the quality of the anchor. Alternatively, there are methods of determining thermochemical properties, in which the energy for a chemical process is measured on an absolute basis. Among the more common of these are the appearance energy measurements, in which the threshold energy for formation of an ionic fragment from an activated precursor is measured. There are mauy differeut methods of activation that can be used. Some of these are discussed here. 

Relative to the most intense photo-dissociation peak ionic fragmentation of the parent molecule is not included. 

Somewhat surprisingly, the pressure dependence of quantum yields from the photolysis of NO at 1236 A, where the primary process is almost entirely photoionization199, is very similar to that observed for 1470-1650 A198. Clearly, recombination of the ionic fragments must lead to an excited state of NO which predissociates upon collision. However, the neutralization reaction... 

Fig. 6.2. El mass spectrum of iodomethane. The molecular ion mainly decomposes to yield ionic fragments representing its major constituent groups, i.e., T, m/z 127 and CH3, m/z 15. Spectrum used by permission of NIST. NIST 2002.

Although stable and neutral bimetallic complexes were obtained from the dicat-ionic fragments and 129 or 130 there was the possibility that reactions with two molar equivalents of a metal-ligand monocation should give rise to trimetallic species. However, reactions of 130 with sources of the cations M (CO)3 (M = Mn, Re), namely [Mn(NCMe)3(CO)3][PF6] and [ReBr(THF)2(CO)3], yielded as products [N(PPh3)2][l,3,6- M (CO)3 -3,6-(p-H)2-l,l,l-(CO)3-2-Ph-c/ow-l,2-ReCBgHT] [M = Mn (156), Re (157)], respectively (Chart 27). ° In these molecules, the exo-polyhedral M (CO)3 moiety is almost certainly bonded to the cluster via two non-equivalent B-H M interactions with an Re-M bond completing... 

The sole gas-phase study on a cationic magnesium cluster examined the photodissociation spectrum of the Mg2(CH4)+" complex . Mg2 is only a minor product (equation 66) while Mg is the main ionic fragment and may arise via either of the processes shown in equations 67 and 68. The latter reaction is predicted to only be slightly more endothermic. 

SIMS—The presence of hydrogen and its isotopes can be determined and some chemical information can be derived from the kinds of ionic fragments sputtered from the surface. 

The mass spectra of chlorine- and bromine-containing compounds clearly show the abundance ratios of the stable isotopes 35C1 37C1 = 3 1 and 79Br 81Br = 1 1 in the molecular ions and those ionic fragments which contain halogens (see Section 9-11). 

Little is known about the mechanism of plasma carbonitriding. It is likely that reactive intermediates such as CHX+ and NR/ are produced41 and that these ionic fragments are eventually incorporated as atomic carbon and nitrogen in the bulk of Sm2Fe17. 

Figure 1S.9 Ionic fragments detected by mass spectrometry analysis during the decomposition of Y(NEt2)4.

Photoisomerization of c/.y-stilbene 191 Ionic fragmentation reaction 191 Cyclopropyl radical ring-opening 192 Ionic molecular rearrangement 193 Ene reaction 196 Thermal denitrogenation 198 Unimolecular dissociation 199 Sn2 reaction 200... 

Fig. 1. Suggested mechanisms for ionic fragmentation of [CpjZrClJzO in the mass spectrometer. (Reproduced, with permission, from Reid et al., 202).

Studies of this nature are just at their inception, with solvent variation and different chromophoric species to be explored. This form of ionic fragmentation chemistry is quite interesting and is highly dependent on solvation structure dependence of these fragmentations can also be investigated in small clusters (n < 6). The opportunity for more experiments and theory here is quite clear. These are perhaps the most solvent rich and dependent processes thus far characterized in clusters. 

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