Oscillating magnetic field effect

Little attention has been devoted to the effects of time-dependent magnetic fields (created by electromagnetic waves) in the absence of a strong magnetic field. Hore and his coworkers [123-125] recently described this effect as the oscillating magnetic field effect (OMFE) on the fluorescence of an exciplex formed in the photochemical reaction of anthracene with 1,3-dicyanobenzene over the frequency range 1-80 MHz. 

Fig. 14.13 The oscillating magnetic field effect (OMFE) in the triplet state radical pair reaction.

The oscillating magnetic field is most effective in causing transitions when its direction is perpendicular to the static field and causes no transitions when parallel to the static field. The reason for this behavior is made clear by an examination of the kinematical properties of a magnetic moment in a static magnetic field. 

This would imply a very simple linear Zeeman effect but, as we show in chapter 8, additional terms describing the nuclear spin rotation interaction and the spin-spin interaction make the system much more interesting. The nuclear spin transitions are induced by an oscillating magnetic field applied perpendicular to the static magnetic field, the perturbation being represented, for example, by the term... 

Double-resonance NMR techniques involve simultaneous irradiation of the sample with two oscillating magnetic fields (Bj and B2) of frequencies v, and v2. This allows us to determine the effect of irradiating one set of nuclei (at v2) while observing the NMR signal of another set of nuclei (at v,). 

It is important to realize that in dipolar relaxation the effect is not primarily to distribute the energy from one of the spins to the other. This would not, on its own, bring the spins to equilibrium. Rather, the dipolar interaction provides a path by which energy can be transferred between the lattice and the spins. In this case, the lattice is the molecular motion. Essentially, the dipole-dipole interaction turns molecular motion into an oscillating magnetic field which can cause transitions of the spins. 

The wave view says that as radiant energy moves away from its source, it has an effect on the space around it that can be described as a wave consisting of an oscillating electric field perpendicular to an oscillating magnetic field (Figure 7.11). 

Magnetic field effect f41 Transient emission and absorption 1251 Quantum oscillations 126,281... 

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