Electron resonance in the rotating reference frame

The magnetic resonance signal of a spin system quantized in the rotating reference frame was observed. The experiment consisted of subjecting the electron spins in solid 2,2 Diphenyl-l-Picrylhydrazyl (DPPH) to a strong r.f. field in the 8 mm. microwave range and observing the Larmor frequency corresponding to the effective field of the rotating frame. Signals from 7 to 52 Mc/s were observed. The results are compared with the theory developed by Redfield for this case, utilizing the concept of a spin temperature. Also observed were the Overhauser and Solid effects, which are two possible ways in which a net polarization of one spin species (in this case the protons in DPPH) may be achieved from the spin-spin coupling to another spin species (the electrons in DPPH). The enhancements obtained (60 and 100 respectively) are higher than those so far reported, although experimental errors make detailed comparisons questionable. The Solid effect is compared with a simplified theory of enhancement utilizing the spin temperature concept, and put forward by I. Solomon.Science, Faculty ofPhysics and Astronomy, Department ofGraduat