Cation mass

Care must be taken not to mistake bands arising from 1 1 or 1 2 van der Waals complexes (e.g. toluene-Arx, x = 1 and 2) for monomer bands. Fragmentation of either the neutral excited state or the cation can cause the 1 1 and even the 1 2 bands to appear in R2PI spectra detected at the monomer cation mass. The van der Waals bands usually appear red-shifted by a constant value from corresponding strong monomer bands. The safest way to identify van der Waals bands is to carry out R2PI scans gated on successive toluene-Ar masses to see which bands disappear at each step. 

Various munerical techniques are used to indirectly obtain solutions to large systems of equations with too many imknowns to solve explicitly. One approach is to solve the equations iteratively. This is done by first assuming that all of the anions are unbound and, hence, their free ion concentrations are equal to their total (stoichiometric) concentrations. By substituting these assumed anion concentrations into the cation mass balance equations, an initial estimate is obtained for the free cation concentrations. These cation concentrations are substituted into the anion mass balance equations to obtain a first estimate of the free anion concentrations. These free anion concentrations are then used to recompute the free cation concentrations. The recalculations are continued imtil the resulting free ion concentrations exhibit little change with further iterations. The computer programs used to perform speciation calculations perform these iterations in a matter of seconds. 

Kuck, D. 1990. Mass spectrometry of alkylbenzenes and related compounds. Part 1. Gas-phase ion chemistry of alkylbenzene radical cations. Mass Spectrometry Review 9 187-233. 

Diffusibility increases with decreasing molecular mass. Dyes with a cation mass of less than 275 migrate well and are suitable for the production of level dyeings, especially in the lighter shades [27],... 

The direct determination of trace elements (Al, Ba, Cu, I, Mn, Mo, Pb, Rb, Se, Sr, and Zn) by ICP-MS in powdered milk was reported [14]. Samples were diluted with a 5 or 10 percent (v/v) water-soluble, mixed tertiary amine reagent at pH 8. This reagent mixture dissociated casein micelles and stabilized liquid phase cations. Mass intensity losses were not observed. The quantitative ICP-MS procedure was applied the standard additions method with a Y internal reference. This direct technique is as fast as the slurry approach without particle size effects or sensitivity losses. 

A mass balance section for the hydrogen sulfide species was added to the anion mass balance calculations when we observed that strong HS complexing of some trace metals sometimes rendered cation mass balance convergence impossible. 

Figure 3. Variation of cation-motion band frequency with cation (a) comparison of frequencies for cations of approximately the same mass but different charge (b) plot of frequency versus inverse square root of cation mass.

Figure 8. The effect of cation substitution on carbonate-H20 fractionation factors at 240°C (O Neil et al. 1969 Kim and O Neil 1997). Note that the change in fractionation factor with cation substitution correlates with both cation radius and cation mass however, the correlation with mass is considerably better suggesting that cation mass is dominant variable.

For these three materials, all have nearly equal anion and cation masses, similar closed shell electronic configurations, and nearly the same ratios of anion to cation ionic radii, —1.35 [64]. Yet aside from the RW vibrational modes, the characteristic vibrational patterns differ significantly. This is especially true for the crossing modes which appear to exist across the Brillouin zone only for RbBr and for the optical modes which are seen in NaF but not in KCl and RbBr. The differences certainly lie with the quite different balance of forces, Coulombic versus short-range repulsions, attributable to the range of sizes and polarizabilities of the ions, particularly of the anions. This absence of similarity also illustrates the importance of close collaborations between theoretical and experimental groups in the analysis and interpretation of HAS data. 

Crossing resonances have been found in nearly all the compounds, but most prominently and across the entire SBZ for KBr and RbBr. The data clearly indicate that nearly equal anion and cation masses are not required for this kind of vibrational motion to exist at the surface. Rather, the existence of these modes is more likely connected with the hybridization of acoustic and optical bulk modes which can occur in isobaric and sometimes also in nonisobaric crystals. 

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