Radio frequency homogeneity

To study NMR spectra of compounds, apparatus is required that consists of three sets of components. These are a radio-frequency transmitter, a homogeneous magnetic field and a radio-frequency receiver. In addition to these, the apparatus includes a unit to sweep the magnetic field over a small range, a mere few parts per million. 

Powerful and highly homogeneous electromagnet, radio-frequency signal generator and detector circuit, electronic integrator, glass sample tubes. 

The first successful electric resonance experiment was reported by Hughes [48] who studied the CsF molecule, an appropriate beam being produced from a hot oven. He used both A and B electric dipole fields, separated by a homogeneous electric C field combined with a radio frequency electric field at right angles to the static field. In order to understand both the deflection and state selection in the dipole fields, as well as the electric resonance spectrum, we first consider the details of the Stark effect. 

CWNMR Throughout the first NMR decades (until the 1970s) the CW technique was practised to determine the resonance state a) frequency sweep the homogeneous magnetic field B0 is static and the radio frequency of an extra oscillating magnetic field... 

The CRAMPS experiment puts a large demand on the NMR hardware (especially on NMR probes), since high-power radio frequency (rf) pulses are applied between each acquisition point. High homogeneity of the irradiation field, as well as careful setup of experimental variables, is required to avoid distortions of the proton peaks. Typical line widths afforded by the CRAMPS experiment are approximately 1 ppm, limiting the application of the CRAMPS experiment to compounds with a small number of well-resolved protons. 

How about some other examples of homogeneously broadened lines The application of high radio frequency power to a transition not only causes saturation (if is sufficiently long) but also causes power broadening for the entire system. When a strongly coupled system, coupled by dipolar interactions, permits spin diffusion and the establishment of a common spin temperature, the attempt to burn a hole in the line will also result in a collapse of the entire line. Dipolar interactions, spin diffusion, and spin temperatures are discussed later in this chapter, as well as in III.C.l. and in IV.D. 

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