Nuclear Magnetic Double Resonance of a Single Nucleus of Spin ½

The nuclear magnetic double-resonance spectrum of a single nucleus of spin ½ is theoretically described by perturbation theory and by the Bloch equations. The perturbation theory correctly predicts all experimental features except line shapes and saturation effects. The description in terms of the Bloch equations provides a clear physical picture of the spin-½ problem. The analysis shows that the macroscopic moment is aligned with the effective field when the strong rf field is not in the immediate vicinity of the Larmor frequency. When the strong rf field is at the Larmor frequency, however, the macroscopic moment is perpendiclar to the effective field. This produces considerable changes in line shapes and intensities as the strong rf field approaches the Larmor frequency. The spectrum in this region is sensitive to the relaxation times, and provides a steady-state method for measurement of relatively short relaxation times. The theory is confirmed by frequency-sweep double-resonance experiments on chloroform saturated with oxygen.