Ion stopping

The main parameters governing the range or energy-loss rate are the energy, E0, and atomic number, of the ion and the atomic number, Z2, of the substrate if we 

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Electronic ion stopping, 14 433 Electronic items, recycling of, 25 871. See also Electronic recycling Electronic waste (e-waste)... 

Nuclear ion stopping, 74 433 Nuclear localization signal (NLS), 26 451 Nuclear magnetic resonance (nmr), 7 7 418 27 278. See also Deuterium nmr... 

While this has been known for a long time, recent developments in heavy-ion stopping [56] stimulated a reevaluation of the Bloch theory which resulted in a major revision of relativistic stopping theory, giving rise to substantial changes in quantitative predictions, in particular for the heaviest ions [9]. 

Figure 12-20 Equilibria in pyruvate kinase reaction as studied by 31P NMR at 40.3 MHz, pH 8.0,15°C. (A-C) Equilibria with low enzyme in levels 15% 2H20. (A) nP NMR spectrum of 1.5 ml of reaction mixture PEP, 13.3 mM ADP, 14.1 mM MgCl2, 20 mM potassium Hepes buffer, 100 mM KC, 50 mM without enzyme. (B) Equilibrium mixture after the addition of 1 mg of pyruvate kinase to the reaction mixture. (C) Equilibrium after the addition of potassium pyruvate (final concentration of 200 mM) to the sample of the spectrum in (B). (D,E) Equilibrium with enzyme concentrations in excess of the substrates. Sample volumes 1.1 ml with 10% 2H20. (D) Equilibrium mixture set up with enzyme (2.8 mM active sites) 2.8 mM PEP 2.4 mM ADP 5.7 mM MgCl2 100 mM potassium Hepes 100 mM KC1. (E) Spectrum after the addition of 50 pi of 400 mM EDTA (pH readjusted to 8.0) to the sample of spectrum D. The EDTA removes metal ions, stopping the catalytic reactions and sharpening the resonances. From Nageswara Rao et al.685...

In the amide reduction scheme on p. 618, the step framed in green gives an iminium ion. Stopping the reaction here would therefore provide a way of making aldehydes from amides. Because these tetrahedral intermediates are rather more stable than those from ester reduction, this can often be achieved simply by carrying out the amide reduction, and quenching, at 0°C (-70 °C is usually needed to stop esters overreducing to alcohols). 

Another way of looking at ionic drift is to consider the fate of any particular ion under the field. The electric force field would impart to it an accelaation according to Newton s second law. Were the ion completely isolated (e.g., in vacuum), it would accelerate indefinitely until it collided with the electrode. In an electrolytic solution, however, the ion very soon collides with some other ion or solvent molecule that crosses its path. This collision introduces a discontinuity in its speed and direction. The motion of the ion is not smooth it is as if the medium offers resistance to the motion of the ion. Thus, the ion stops and starts and zigzags. However, the applied electric field imparts to the ion a direction (that of the oppositely charged electrode), and the ion gradually works its way, though erratically, in the direction of this electrode. The ion drifts in a preferred direction. 

The AO results may also be used for benchmark tests of simpler models. In this context we have also checked a simple non-perturbative model, the UCA. This model includes the main features of fast heavy-ion stopping, as is shown by comparison with large-scale AO results for the impact-parameter dependent electronic energy transfer. The computation of the energy loss within the UCA is much simpler and by many orders of magnitude faster than the full numerical solution of the time-dependent Schrodinger equation. 

The non-linear scheme described in this work is implemented in the computer program Histop (Heavy Ions Stopping), which is freely available from the web page indicated in Ref. [61]. 

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