Deuterium nucleus, properties

The following paragraphs provide an overview of some important NMR experiments. In analogy to the intuitive picture of a spin I = 1/2 precessing in space, the behaviour of the deuterium nucleus with a spin-1 will be visualized here in a higher-dimensional coordinate system. Some excellent reviews are recommended for further reference, which cover the special properties of spin-1 in more depth [3, 14]. 

Hydrogen as it occurs in nature is predominantly composed of atoms in which the nucleus is a single proton. In addition, terrestrial hydrogen contains about 0.0156% of deuterium atoms in which the nucleus also contains a neutron, and this is the reason for its variable atomic weight (p. 17). Addition of a second neutron induces instability and tritium is radioactive, emitting low-energy particles with a half-life of 12.33 y. Some characteristic properties of these 3 atoms are given in Table 3.1, and their implications for stable isotope studies, radioactive tracer studies, and nmr spectroscopy are obvious. 

Because isotopes of the same element have the same number of protons and the same number of electrons, they have essentially the same chemical and physical properties. However, the mass differences between isotopes of hydrogen are comparable to the masses themselves, leading to noticeable differences in some physical properties and slight variations in some of their chemical properties. Hydrogen has three isotopes (Table B.2). The most common ( H) has no neutrons so its nucleus is a lone proton. The other two isotopes are less common but nevertheless so important in chemistry and nuclear physics that they are given special names and symbols. One isotope (2H) is called deuterium (D) and the other ( H) is called tritium (T). 

It is a fundamental property of atomic particles, such as electrons, protons, and neutrons, to have spins. Spins can be classified as + or spin. For example, a deuterium atom, H, has one unpaired electron, one unpaired proton, and one unpaired neutron. The total nuclear spin = j (from the proton) + j (from the neutron) = 1. Hence, the nuclear spins are paired and result in no net spin for the nucleus. For atoms such as H,... 

For example, there are three distinct kinds of hydrogen atoms, commonly called hydrogen, deuterium, tritium. (This is the only element for which we give each isotope a different name.) Each contains one proton in the atomic nucleus. The predominant form of hydrogen contains no neutrons, but each deuterium atom contains one neutron and each tritium atom contains two neutrons in its nucleus (Table 5-2). All three forms of hydrogen display very similar chemical properties. 

Figure 1. Representation of the properties of a nonquadrupolar and a quadrupolar nucleus. The charges around the nucleus represent those of its molecular environment. The electric field gradient tensor, qae, is expressed in the coordinate system of the molecule. Usually, the z-axis lies along the carbon-deuterium bond e is the charge on the electron, h is Planck s constant, and Q is the quadrupole moment. For axial symmetry, only q, is required to express the quadrupole coupling constant.

Natural hydrogen in molecular or combined forms contains about one part in 2000 of DEUTERIUM, symbol D, an isotope of hydrogen that contains one proton and one neutron in its nucleus. The artificially created radioactive isotope TRITIUM, symbol T, has one proton and two neutrons. Although the effect of isotopes on chemical properties is normally small, in the case of hydrogen the difference in mass number leads to a lowering of some reaction rates, a phenomenon known as the isotope effect . 

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