Ion-solvent cluster

The fonnation of clusters in the gas phase involves condensation of the vapour of the constituents, with the exception of the electrospray source [6], where ion-solvent clusters are produced directly from a liquid solution. For rare gas or molecular clusters, supersonic beams are used to initiate cluster fonnation. For nonvolatile materials, the vapours can be produced in one of several ways including laser vaporization, thennal evaporation and sputtering. 

Picosecond time regime kinetic studies of proton transfer are coming into vogue (28, 29, 30), particularly for intramolecular processes that can be very fast. Bound to play an increasingly important role in the elucidation of proton transfers are the gas phase ion-solvent cluster techniques that reveal dramatically the role played by solvent molecules in these reactions (M, 32). 

Fig. 3.6 Destruction of the ion solvent cluster by CID is rarely possible, as this is followed by a reduction of Cu(ll) to Cu(l) and generation of only few Cu(ll)-solvent-cluster. These Cu-based clusters are easily identified by the isotope pattern from Cu/ Cu. (From Schramel et al. 1999, with permission from Springer.)...

When a gas expands into a vacuum, strong cooling takes place. This effect is widely used for the spectroscopic study of cold molecules. When a mixture of ions and gas and water or solvent vapor expands into vacuum the cooling in the expansion region will promote the formation of ion-solvent clusters that may be so large that they fall outside the mass range of the mass analyzer ... 

The undesired formation of ion-solvent clusters is due to the temperature drop in the expansion into the vacuum system. By heating the source, or using of a heated tube for the passage of sample ions from the source into the vacuum, the temperature in the expansion region will not reach such a low value, and ions may cluster with only a few molecules, which can be removed in the expansion region by moderately energetic collisions. 

The solvation (including hydration) of ions in the gas phase is described in Section 2.1.2 in terms of the stepwise Gibbs energies and enthalpies of the formation of ion/solvent clusters. The absolute values of these quantities diminish as the number... 

Thermal treatment and the nature of the casting solvent can also affect the deformation modes achieved in strained films of ionomers. For example, in films cast from polar dimethylformamide (DMF), the solvent interacts with ion-rich clusters and essentially destroys them, as is evident form absence of a second, higher temperature loss peak in such samples. As a result, even in a cast DMF sample of Na-SPS ionomer of high ion content (8.5 mol%), the only deformation mode observed in tensile straining is crazing. However, when these films are given an additional heat treatment (41 h at 210°C), shear... 

In the latter case the dopant is ionised, interacts with the solvent and, subsequently, solvent clusters interact with the analyte. Molecular and protonated molecular ions are observed, indicating that ionisation can occur via proton (toluene) and electron transfer (acetone). 

A. Charge Reduction (Charge Separation) on Desolvation of Multiply Charged Ion-Solvent Molecule Clusters... 

Another subsidiary class of clusters is often referred to as "naked. This class, which includes ions such as Bii+, Snjj-, GeJ- and SnJ-, is largely unexplored, but clearly its chemistry will be dominated by large ion-ion or ion-solvent interactions. Such clusters will not be considered in this account. 

It was pointed out that the ratios between the protonated, sodiated, and potassiated forms of the molecular ions, the clusters and the doubly charged ions exhibited relatively high day-to-day variations. Obviously, changing contents of competing cations derived from the sample as well as from impurities in the solvents interfered with the formation of a desired species. 

When APCI in used in combination with the normal phase LC, the nitrogen molecular ion will enter into a charge-transfer reaction with the organic solvent. Ion-molecule reactions lead to protonated solvent clusters that will react by proton transfer with the analyte molecules, forming [M + H]+ ions. 

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