Lamor frequency

Figure 5.3 Depiction of four spinning nuclei. Spinning nuclei simultaneously spin and precess at a Lamor frequency, v j therefore angular momentum vectors (red arrows) map out processional cones. In the absence of any external magnetic field, vectors align relative to arbitrary z-axes. According to quantum mechanical rules, magnitude of angular momentum / is determined by spin quantum number I and a spinning nucleus can exist in any one of 2/ -I- 1 spin states.

Figure 5.10 Radio frequency variation of My(t) transverse magnetisation observed, acquired and stored digitally with time is known as a Free Induction Decay (FID). Stored FID either singly or averaged, are processed by fourier series transformation (FT) from time domain signal information, SnoCti), into frequency domain (spectral) information, /nmr( i)- Only chemically equivalent nuclei without spin-spin coupling and with an equivalent Lamor frequency, V, are being observed here hence only a single signal will result of frequency Vi.

Figure 2 The tilting of Mo into the x -y frame due to the application of RF at the Lamor frequency

FID. The FID which results when a single type of (e.g. a proton decoupled singlet) is shown in Fig. 5a for P(OMe) and appears as an exponentially decaying sine wave whose frequency is the difference between the center frequency of the excitation pulse (sometimes called the carrier wave) and the Lamor frequency of our signal. For the case where several absorptions occur the decay will appear somewhat differently such as in Fig. 5b for which the... 

This difference in the Lamor frequency of the electron spin gives the recombination product an excess of a nuclear spin which will be observed as emission in the CIDNP spectrum. The converse is true for escaped products, which will have an excess of p nuclear spins and wiU be observed as enhanced absorption in the CIDNP spectram. Obviously, for a singlet correlated radical pair the opposite is true with an excess of p and a nuclear spins observed on the recombination and escaped products respectively. 

Influence of the nuclear spin I on the time dependence of the atomic spin direction can be neglected. The precession frequency of the atomic spin S is such that the nuclear spin reacts only to the quantum value S. If the value of is maintained for an average period of time tg which is long compared with the nuclear Lamor precession time I/col (i.e. cottg > 1) and the latter is long compared with the lifetime of the Mdssbauer event (i.e. > 1) then... 

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