Proton spin states, inversion

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-... 

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... 

All nuclear multiplet structures due to coupling of nonequivalent nuclei are, as noted earlier, subject to effects on line shapes by chemical or positional exchange. For those multiplet structures arising from coupling of nuclei, one of which has a nonzero nuclear quadrupole moment, effects of quadrupole relaxation must be considered. For example, if a proton or fluorine atom is bonded to a nitrogen nucleus (I = 1), a triplet resonance will be expected in the proton or fluorine spectrum. For observation of this fine structure it is necessary that the lifetimes of the nuclear spin states of nitrogen (m = 1, 0, —1) be greater than the inverse frequency separation between multiplet components, i.e., t > l/ANx (106). The lifetimes of N14 spin states can become comparable to or less than 1 /A as a result of quadrupole relaxation. When the N14 spin-state lifetimes are comparable... 

The line width is sensitive to tNH4+ but this is one-quarter the inverse rate constant because each transfer involves only one proton. Further, each proton has one chance in three of attaching itself to a nitrogen in the same spin state. The chemical rate constant is therefore given by... 

Fig. 7. A C-13 relaxation time measurement of solid state wetted cellulose acetate (6% by weight water) using the inversion recovery (IR) method at 50.1 MHz and spinning at 3.2 kHz at the magic angle (54.7 deg) with strong proton decoupling during the aquisition time (136.3 ms), (upper part of the Figure). Tau represents the intervals between the 180 deg (12.2 us) inverting and 90 deg (6.1 us) measuring pulse. 2200 scans were collected and the pulse delay time was 10 s, Cf. Table 3 and Ref.281...

---