Integer spin nuclei

The first-order frequency shift vanishes for m = 3, which means that the central transition for noninteger spin nuclei is not affected to first order by quadrupolar interactions (see Fig. 2). It is clearly advantageous to work with these, as the — 1 <- 0 and 0 <-> 1 transitions for integer spin nuclei are always shifted. 

Table 1.3. Standard reference substances for the quadrupolar and integer-spin nuclei, with compounds commonly used as secondary references and their shift relative to the primary reference.

It has been pointed out that the central ( 2, transition does not experience any first-order quadrupole interaction. The absence of first-order broadening effects is a general property of symmetric (m, - m) transitions. There are cases where this can be a distinct advantage, the most direct instance being for integer spin nuclei (e.g. D and both 1=1) where there is no ( /2, — /2) transition. The main problem is to excite and detect such higher-order transitions, for which there are two separate approaches. The sample may either be irradiated and detected at the multiple quantum frequency (called overtone spectroscopy) or the MQ transition can be excited and a 2D sequence used to detect the effect on the observable magnetisation. 

The opposite extreme regime, when co coq, involves the so-called soft or selective RF pulses. In this case, pulses of long duration and low power can be used to excite just one of the transitions, which is achieved by a suitable choice of the resonance offset (72) and also of the pulse length. The main aspect to be considered here is that each transition has associated with it a specific frequency and a different effective nutation fi equency, which depends on the values of I and m. For selective excitation of a transition between the levels m + and m, it is found that the ideal soft jr/2 pulse must be shorter than the corresponding hard itjl pulse (which excites all transitions) by a factor of -3-1) —m m 1). For excitation of just the central transition (1 /2 -1 /2) for half-integer spin nuclei, the... 

Scenario 1 boson nuclei (that is, integer spin nuclei)... 

Two books entitled SoHd-State NMR Techniques and Nuclear Magnetic Resonance Spectroscopy of Cement-Based Materials , have been published. A number of reviews have appeared, entitled Solid-state nuclear magnetic resonance , Solid-state NMR spectroscopy of non-integer spin nuclei , A... 

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