Nucleus isotopes

The iron group elements. Figure 3 displays the isotope ratios for this group. As a general result, the most neutron-rich isotope nuclei of this group display the largest variations relative to the other isotopes. Deficits are seen for Cl, and excesses for EK141. 

A kinetic isotope effect observed by a single reactant, having isotopic atoms at equivalent reactive positions, which reacts to produce isotopomeric products with a nonstatistical distribution. The pathway favored will be the one having lower force constants for the displacement of the isotopic nuclei in the transition state. 

Isotopes Nuclei with same number of protons but different number of nucleons (proton + neutron) are... 

Fig. 2. Scattering cross sections for pt with a hydrogen isotope nuclei from Refs. [12,18], showing the Ramsauer-Townsend minimum at around 10 eV for pt+p pt(F) +t cross sections plotted include both elastic and spin exchange reactions, where pt(0) is the singlet state and pt( 1) is the triplet state...

Similar relations can be used in comparing two isotopes of the same element. By observation of the same transition frequency of the two isotopic nuclei in one compound, one can assume a constant electric field gradient (that is, no measurable influence of the nuclear mass and the nuclear charge distribution on the core electrons). 

Nuclear magnetic resonance (NMR) is a unique technique that depends on the magnetic nature of a few isotopic nuclei, primarily H, F, and R... 

Natural lipids consist of the elements hydrogen, carbon, phosphorus, nitrogen and oxygen. Some isotope nuclei of these elements can be detected by NMR. The low natural abundance of and prevents the routine application of NMR to these elements without use of labelled substances, but H, and PNMR spectroscopy are used routinely. Many instruments are equipped with a so-called QNP (quattro nuclei probe) for sequential NMR analysis of H, P and without changing hardware. 

Isotope effects are usually based on the differences between the masses of the atoms and therefore they are referred to sometimes as isotope-mass effects (the so-called mass-independent isotope effects, for example, the magnetic isotope effects, which are due to the differences between the nuclear spins of isotopes, will be discussed in O Sect. 15.8). The geometrical and electronic structures of isotopic molecules are much the same because isotopic nuclei differ only in the number of neutrons, while it is the number of protons that determines the nuclear charge and thus the electron distribution and molecular structure. This fact leads to a great simplification in theoretical calculations of isotope effects. 

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