Protons spin states

This ratio indicates that at equilibrium 50.0379% of the electrons are in the lower (ms = -j) state, while 49.9621% are in the upper state. Or, to put it another way, of one million electrons, there are 758 more in the lower state than in the upper state. Although this may seem like a very small difference, it is 38 times greater than the difference in proton spin state populations, a difference of only 20 nuclei per million at 2.35 T (Example 2.8) ... 

The pulse sequence has a basic polarization transfer portion (Figure 3) which produces a net inversion of one of the proton spin states. Following an X nucleus 90° pulse there exists enhanced magnetization in the X multiplet. The signal enhancement is proportional to the ratio of the mag-netogyric ratios of the two nuclei involved, a factor of 4 for and 10 for l N for X-1h experi-... 

If small incremental quantities of copper(II) ion are added to a 0,5 M solution of ethylamine, at approximately 10 M copper ion only the peak will be broadened and at higher concentrations will eventually disappear, showing that those proton spin states have been rapidly relaxed by the paramagnetism of the nearby copper ion. If EDTA is now added, the peak reappears, showing the copper ion to be tied up in a slow-exchanging complex. 

Energy levels and transitions for the proton spin states of formaldehyde. On the left are the levels obtained with neglect of spin-spin interaction, and they are labeled by the ra, quantum numbers of the two protons. The middle level is doubly degenerate. If spin-spin interaction is treated with first-order degenerate perturbation theory, the levels on the right result, with an assumed size of the coupling constant, /. A transition from the 7 = 0 state to an / = 1 state would measure /, but that is a forbidden transition. No splitting of the line in the spectrum occurs. 

This special pulse sequence uses strong nonselective pulses and gives general enhancement rather than specific sensitivity enhancement, as in SPT. The pulse sequence has a basic polarization-transfer portion that produces a net inversion of one of the proton spin states. Proton transverse magnetization is created by the initial proton 90° pulse and precesses for a period t. The magnetization is then refocused as a spin echo at a time 2r by the action of a 180° proton pulse. Application of a 180° pulse at the midpoint of the 2r delay ensures that the echo is modulated by the scalar coupling, 7ch- If t is chosen to be equal to 1/(4Jch) then at time 2r, the... 

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