Oscillator magnetic-dipole-allowed

The electric dipole selection rule for a hannonic oscillator is Av = 1. Because real molecules are not hannonic, transitions with Av > 1 are weakly allowed, with Av = 2 being more allowed than Av = 3 and so on. There are other selection niles for quadnipole and magnetic dipole transitions, but those transitions are six to eight orders of magnitude weaker than electric dipole transitions, and we will therefore not concern ourselves with them. 

This method uses the dipole field setup by an oscillating magnetic sample in a uniform magnetic field. The sample oscillation is driven by a loudspeaker that vibrates a sample holder rod, the other end of which moves the sample between the magnet poles. A permanent magnet reference sample is vibrated on the same rod. Separate induction coils, oriented with their axes parallel to the vibration monitor to allow phase-sensitive detection, monitor the sample and reference. Only a relatively small sample can be placed fully within a uniform field, but measurements on small single crystals are readily made with this apparatus. Measurements on anisotropic crystals can be made by remounting the crystal to vary the orientation with respect to the sample rod. 

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