Hyper-nuclei

The mechanism is similar for the production of multi-hyper nuclei A, E, S, Q). Meson field theory predicts also for the A energy spectrum at finite primary nucleon density the existence of upper and lower wells. The lower well belongs to the vacuum and is fully occupied by yl s. 

These atomic orbitals, called Slater Type Orbitals (STOs), are a simplification of exact solutions of the Schrodinger equation for the hydrogen atom (or any one-electron atom, such as Li" ). Hyper-Chem uses Slater atomic orbitals to construct semi-empirical molecular orbitals. The complete set of Slater atomic orbitals is called the basis set. Core orbitals are assumed to be chemically inactive and are not treated explicitly. Core orbitals and the atomic nucleus form the atomic core. 

This is one of several reactions of this type in which an organic negative radical-ion and its parent molecule react in the presence of an alkali metal. It is found, rather interestingly, that the rate coefficients depend on the nature of the metal. To account for this, it has been postulated that the metal is involved in a bridging role in the activated complex, e.g., dipy.. K" ". . dipy for the case of 2,2 -dipy-ridyl (dipy) A more extreme case of this association between the radical-ion and the ion of the alkali metal used to form it occurs in the reaction of benzophenone with its negative ion. The spectrum of (benzophenone)" in dme has many hyper-fine lines caused by the interaction of the free electron with the and, when the metal is sodium, the Na nuclei. When benzophenone is added, the structure, due to the proton interaction, disappears and only the lines associated with the sodium interaction remain. To account for this, it has been suggested that the odd electron moves rapidly over all the proton positions too fast for the lines characteristic of the electron in the different proton environments to be seen), but relatively slowly from one sodium nucleus to another. Seen another way, this means that the transfer of an electron from molecule to molecule is associated with the transfer of the cation . ... 

Sahu, A., Sninsky, C.A., Phelps, C.R, Dube, M.G., Kalra, P.S. Kalra, S.P. (1992b) Neuropeptide Y release from the paraventricular nucleus increases in association with hyper-phagia in streptozotocin-induced diabetic rats. Endocrinology 131, 2979-2985. 

From the ENDOR spectriun with these two lines, one can derive both the hyper-fine splitting constant. A, and the nuclear factor, gi (characteristic of given nucleus) with high accuracy. 

The change of the nuclear transition probability due to the electron spin is usually called hyperfine enhancement s and has first been discussed by Abragam The hyper-fine enhancement may be considered classically as originating from the modulation of the magnetic field Be produced by the electron at the nucleus. The size of Be is determined by the hf interaction between the electron and the corresponding nucleus. The field B " which induces nuclear transitions, is then given by the vector sum of B2 and the component of Be which oscillates with the same frequency as the applied field. 

The appearance of an ENDOR spectrum depends on the relative size of the hyper-fine coupling (hfc) and the NMR frequency vn. For a nucleus with nuclear g-factor = 5.586 a frequency of vh = 15 MHz is characteristic for... 

Fig. 2.23 Schematic HYSCORE spectrum showing (a) the HYSCORE sequence, (b) the 2D time-domain modulation signal, (c) the 2D HYSCORE spectrum and (d) the contour plot of a single crystal sample for an 5 = Vi species containing a H nucleus with an axitilly symmetric hyper-fine coupling. The magnetic field is at an angle 0 = 10° with the A axis. The nuclear Zeeman frequency vh 15 MHz is larger than the hyperflne coupling, i.e. Ai I < A < 2 vh...

The PES found via the adiabatic approximation described in the previous section portrays the hyper landscape over which a nucleus moves, in the classical sense, while under the influence of other nuclei of a particular system. This is useful for describing vibrations or reactions. Electronic contributions have been averaged into each point on the PES, and their effect considered for that particular nuclear... 

Consider the ethyl radical as an example (Fig. 4). Since its 2p-orbital has a node at the nucleus, no contact interaction is likely to take place in this organic free radical. However, the spin exchange interaction of the unpaired electron of the 2p-orbital with the electrons of the spin density at the nucleus. Furthermore, this interaction causes the electron spins to polarize at each a-proton and leads to a hyperfine structure. Accordingly, the hyper-fine splitting constant a for the a-proton is proportional to the unpaired electron density at the radical center. Thus we obtain the relation... 

This relation is based on the assumption that the k value is the same for both isotopes. Since k, in a first approximation, is only related to the electronic shell, such an assumption is very reasonable. However, small differences in k can occur due to electron penetration into the nucleus (s-electrons). This results in a deviation from the relation in (7.21), or a so-called hyper fine anomaly. However, this anomaly is generally less than 1%. The dipole moment of the nucleus can also be determined directly by high-precision ABMR measurement in high magnetic fields, by observing the small direct contribution from the nucleus. 

An electric quadrupole transition is a y-ray transition between the hyperfine multi-plets of the nucleus in its ground and excited states. Only those nuclear states with 7 > 1 /2 have a nuclear quadrupole moment and hence show quadrupole hyper-flne splitting. Thus, it is often possible to observe a quadrupole interaction in the Mdssbauer spectrum that derives from the excited nuclear state. 

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