Ion attachment reactions

The first direct demonstration of the applicability of alkali ion attachment reactions using a sodium cation emitter as a novel and sensitive technique of ionization for ion trap mass spectrometry was made with an ion trap mass spectrometer equipped with an external ion source to generate the reagent Na ions [28]. The combination of alkali metal ion attachment with an ion trap may well represent a noticeable improvement in the selectivity and sensitivity of current GC ion trap technology, and may enlarge the scope of use of this type of mass spectrometer. 

Ion trap mass spectrometers demonstrate complete apphcabihty to these alkali metal ion attachment reactions due to their in-time confinement capability, which provides a high efficiency for alkali ion attachment reactions compared to conditions in a classical quadrupole ion source. This method should be of general interest to those needing to solve problems involving organic pollutants, samples diluted in a matrix, pyrolytic products and samples that are of environmental concern, in situations where classical chemical ionization techniques are not always satisfactory due to their structure-dependent responses. One of the main advantages of sodium ion attachment reactions for such analysis is that the ionization conditions are not pressure dependent, unlike conventional Cl ionization processes. 

More common are association or ion attachment reactions (Equation 12.3), which can be followed by dimerization or clustering (Equation 12.4) with elevated concentrations of M and collisional stabilization ... 

Fig. 5.1 Schematics of a quadrupole mass spectrometer with a LR ion attachment reaction chamber. Any stream from sample inlet system whose components one want to analyze is directed to the reaction chamber. RP rotary pump, IMP turbomolecular pump, QMS quadrupole mass spectrometer...

Faye T, Brunot A, Sablier M, Tabet JC, Fujii T. Sodium ion attachment reactions in an ion trap mass spectrometer. Rapid Commun Mass Spectrom. 2000 14 1066-73. 

Consideration of work by Buchel nikova (4) on the dissociative attachment of electrons to HC1 leads to the conclusion that k4 is given approximately by k4 10-10 e 20 mtRT cm.3 molecule-1 sec.-1 Since K 4 2 X 10-3 el8 miRT at 2000°K., 4 10 13 cm.3 molecule-1 sec.-1 This is considerably smaller than rate constants for other exothermal ion-molecule reactions, which probably reflects the importance of participation of molecular vibrational energy in such reactions. Remember, however, that the uncertainty in 4 is probably at least an order of magnitude. 

The reaction is exothermic if the energy needed to break the bonds is less than the energy released when the ions attach to water. 

Figure 7. Ion source and reaction chamber for the study of ion-molecule reactions at different temperatures. Notation used is same as in Figure 4 except CB = copper block, EL = electrode attached to pressure reducing capillary, TC = thermocouple, TS = thermal shield, ISP = evacuated space reduces thermal conductivity from CB to flange. From Klassen, J. S. Blades, A. T. Kebarle, P. ). Am. Chem. Soc. 1996, with permission.

Huang and Freiser (132, 133) were able to prepare exohedral metal C60 ions [MC60]+ by direct reaction of the bare metal ions Fe+, Ni+, Co+, Cu+, Rh+, and La+ with Cgo vapor produced from a heated probe. The [MC60]+ ions when subjected to low-energy collision-induced dissociation with argon all produced the Cg0 ion. These results show that the metal ions attach to the outer surface of C60. The exohedral metallofullerene ions differ from the endohedral metallofullerenes produced by laser ablation of metal oxide-graphite mixtures and support the observations of Smalley and co-workers (148) who found that endohedral metallofullerene ions dissociate by loss of C2 units. 

For attachment to CO2, the rate constant clearly shows a dependence on AGr(/). However, for attachment to other solutes like aromatics, the dependence on AGr(l) is not yet clear. Questions remain like what is the role of reorganization energy, which can be large even in nonpolar solvents [142] it was pointed out earlier that there is considerable density augmentation around the negative ions formed in attachment reactions. For solvents like TMS, rates maximize for values of AGr(/) near -0.7 eV what rate is to be expected for large values of -AGr(/) Is the high rate observed for Cgo typical or the low rate for quinones more typical Further study is needed to resolve these questions. 

Negative ions are also produced by electron bombardment through a variety of electron attachment or dissociative capture processes (Dillard, 1973). They may also be generated indirectly as the result of an ion-molecule reaction. The cross-sections for negative ion formation are at least an order of magnitude less than those for positive ions, a fact which accounts for the much weaker ion currents that are produced. Some of the common precursors for well-known negative ions are shown in (6)—(13). For several of these... 

In heterocyclic chemistry it can be misleading to speak of covalent addition to mean both a product of an addition reaction, such as the hydration of a neutral substrate (i.e., transformation of pteridine to the 4-hydroxydihydro derivative),20 and a product of an attachment reaction, such as the reaction of the hydroxide ion with the ring carbon of a heteroaromatic cation.21... 

In the presence of RO ions several oxo derivatives related to 5-nitrouracil undergo the attachment reaction at position 6.42,51 The formation of adducts 18a-18h is favored by the presence of the nitro group. As usual, the forma-... 

In the case of the reactions with the aromatic compounds, the nature of the reaction was established by observing the optical absorption spectrum of the transient product. Thus, in the reaction with diphenyl and p-terphenyl, the observation of the spectra of the mononegative ions (3) of these compounds establishes the occurrence of an attachment reaction. The rate constants for the reactions with diphenyl, naphthalene, p-terphenyl, and naphthacene increase in the order of increasing electron affinities of these compounds. In the case of the attachment reaction to oxygen, no attempt has been made to study the product ion in the alcohols. We have, however, obtained (7) the absorption spectrum of the O2 ion in aqueous solution. 

As in the case of the positive ion chemistry, the problem is to describe the chemical steps which convert the primary negative ions to the observed clusters. The primary negative ions can only be O- and 02 formed in the electron attachment reactions ... 

At lower altitudes where significant concentrations of ozone exist, O- ions are generated by dissociative attachment [reaction (10b)]. These electron attachment processes and the laboratory techniques used to determine their rate coefficients were reviewed some time ago by Phelps1 S4 In the stratosphere and troposphere, negative ions can also be generated by dissociative attachment reactions of thermalised electrons with pollutants1 s5,1561 such as the freons e.g. 

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