Multicharged ion

Normally, a range of values for n is found, each molecule (M) giving a series of multicharged ions. For example, a series... 

This last m/z value is easy to measure accurately, and, if its relationship to the true mass is known (n = 10), then the true mass can be measured very accurately. The multicharged ions have typical m/z values of <3000 Da, which means that conventional quadrupole or magnetic-sector analyzers can be used for mass measurement. Actually, the spectrum consists of a series of multicharged protonated molecular ions [M + nWY for each component present in the sample. Each ion in the series differs by plus and minus one charge from adjacent ions ([M + uH] + n -an integer series for example, 1, 2, 3,. .., etc.). Mathematical transformation of the spectrum produces a true molecular mass profile of the sample (Figure 40.5). 

This inlet/ion source is a simple system with no moving parts and yields many ions from the original dissolved sample. Even more attractive is the tendency for electrospray to produce multicharged ions, a benefit that makes accurate measurement of large relative molecular masses much easier. 

When multicharged ions are formed, the simple rule of thumb used widely in mass spectrometry that m/z = m because, usually, z = 1 no longer applies for z > 1 then m/z < m, and the apparent mass of an ion is much smaller than its true mass. Accurate mass measurement is much easier at low mass than at high, and the small m/z values, corresponding to high mass with multiple charges, yield accurate values for the high mass. 

Electrospray ionization (ESI) produces a series of multicharged ions that can be transformed into an accurate molecular mass for proteins with masses of tens of thousands. 

In accordance with previous investigations [8,9], Aese experiments have shown a quite different behaviour for N (ls )than for other multicharged ions such as the isoelectronic ion [10. The single-electron capture process has been shown to be dominant on the n = 3 levels and in particular on the 3s level for collision energies lower than 50 keV. A high probability of double capture has also been observed characterized by an intense peak at X = 76.5 nm attributed to the 2s > 2s 2p P transition [4,5,7]. Furthermore,... 

ESI is also able to ionize not only small but also elephant molecules. In this case multicharged ions are produced (see Section 2.6.2.2). A typical ESI spectrum of a large molecule is shown in Figure 2.21. 

Onda found a standard deviation of 0.052J./mol for his complete set of data, including multicharged ions. These correlations thus provide a coefficient for gases in ammonium bicarbonate that may be in error by more than 0.05 Jl/mol Onda s coefficients for gases in ammonium hydrosulfide are of unknown origin and accuracy, and coefficients for ammonium carbamate are not provided. In short, this type of correlation does not provide the needed information. 

Avoid CMP chemistry that involves multicharged cations. Such chemicals compress the double charge layer and activate slurry agglomeration and process defectivity. Ions such as Al and Fe may initiate agglomeration and scratching at concentrations as low as lO to 10 M. 

QED CALCULATION OL HEAVY MULTICHARGED IONS WITH ACCOUNT EOR CORRELATION, RADIATIVE AND NUCLEAR EEEECTS... 

Detailed analysis of the VP and SE energy eontributions shows that for ions with small Z the QED eontribution is not signifieant, but with growth of Z (Z > 40) the QED contribution becomes very important. Moreover, for heavy and superheavy ions its role is of main importance. Now let us consider the role of the nuelear finite-size effeet. As calculations show, for multicharged ions with Z < 20 its contribution is very small, but for ions with Z > 70 it can equal the vacuum polarization contribution. In Table 3 there are displayed the results of calculations for the nuelear eorrection to the energy of low transitions for Li-like ions. Our calculations also show that a variation of the nuelear radius by a... 

At v < v0Z213 the effective charge zeff is proportional to v/v0. So the dependence of se on velocity in this case is solely due to the logarithmic term in formula (5.2), which decreases as the ion s velocity falls. Consequently, as the ion slows down, se must also decrease, that is, its behavior is exactly opposite to the case of protons and alpha particles, where se increases as the particle s velocity falls, until it approaches Bragg s peak. In Section VIII.D we will show how this particuliarity affects the structure of the track of a multicharged ion. 

Characteristics of Tracks of an Alpha Particle and of a Multicharged Ion 127I in Water ... 

For each parameter of the track the top number corresponds to the alpha particle and the bottom number-to the multicharged ion 127I. N, and Ns are, respectively, the number of ions and the number of delta electrons the particle produces per 1 nm of its path length n] is the average concentration of ions in the core of the track n, is the average concentration of ions in the track and rsh is the radius of the track shell. 

Fig. 20. Schematic diagram of the changes in the characteristics of the track of heavy charged particles with retardation (a) the alpha particle (b) a multicharged ion.

The primary effect of a multicharged ion is the ionization of practically all the molecules in a cylinder with diameter 0.7 nm (see estimates made in Ref. 335). Most of the energy of secondary electrons is also localized inside the core, and so the number of ionization events inside the core of the track of a multicharged ion exceeds the number of molecules in it. Consequently, practically every molecule of the core is ionized and... 

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