Dimeric ion

Dimeric ion. An ion formed either when a chemical species exists in the vapor phase as a dimer and can be detected as such, or when a molecular ion can attach to a neutral molecule within the ion source to form an ion such as (2M)+, where M represents the molecule. 

Both benzene dimer ion radicals were a subject of a recent theoretical study (166). 

Similarly, Ervin and co-workers have measured acidities of organic molecules by measuring the energy for endothermic proton transfer reactions between acids and anionic bases." " Alternatively, it is possible to use competitive CID of proton-bound dimer ions." Nominally, these are relative approaches for measuring acidities, as the measured acidities depend on the properties of the reference acids or bases. However, it is usually possible to select references with very accurately known acidities (such as HE, HCN, or HCl), such that the accuracy of the final measurement depends predominantly on the accuracy of the threshold energy determination. 

In the following section, we will reexamine some earlier recombination measurements to see if third-body effects may have played a role. The rare gas dimer ions provide a good starting point. 

The various observations leave little doubt that recombination of rare-gas dimer ions can produce excited atoms, but it is quite possible that formation of radiating excited states occurs only in a small fraction of recombination events. If this is true, then the observed line shapes do not reflect the dominant recombination mecha-... 

Mass losses of more than one monomer unit appear as unresolved shoulders. The loss of up to five methanol monomers from the protonated octamer is observed. Another peak was found to correspond to loss of water from the protonated methanol dimer ion via the dehydration reaction,... 

From the ESI-FIA-MS(+) spectrum in Fig. 2.5.10(b), the amphoteric amine oxide surfactants ([M]+ ions at m/z 230, 258 and 286) and their dimeric ions ([2M - H]+ at m/z 459 and 487 (230 combined with 258)) could be recognised. The identity of the amine oxides was confirmed by recording product ions of the [M]+ ion at m/z 230 before the parent ion scan of fragment m/z 58 and vice versa was recorded for confirmation. This spectrum contained the A m/z 28 equally spaced characteristic amine oxide homologue ions at m/z 230, 258 and 286. 

Benzylideneacetone reacts with lithiated phenylacetonitrile under kinetic control, in THF and media that favour association, to give 1,2- and 1,4-adducts in proportions which are directly related to concentrations of monomeric and dimeric ion pair species, respectively." An attempt has been made to explain the different regioselec-tivities towards a,-unsaturated carbonyl compounds, including cyclic a-enones and cinnamaldehyde, in terms of intermediate complex formation. 

The association reaction involving excited states, which has been studied most extensively is the benzene dimer ion formation,21,194-203... 

All such reactions are characterized by a lowering of the cross section as the internal energy of the adduct is increased. The lifetime of the benzene dimer ion, as well as those of similar adduct ions, is very sensitive to its internal energy since it is very loosely bound (it has a binding energy of 8 kcal/mole). Increasing the product-ion internal energy by vibrational excitation of the reactant readily promotes the dissociation back into reactants. 

A particularly interesting group of reactions that fall in this category are those of the helium dimer ion, He (Ar22 ). It was suggested some time ago that reaction of this species with nitrogen,... 

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