Abstract
Dynamic polarization experiments have been carried out in dilute solutions of sodium in liquid ammonia (mole ratio R > 130) at room temperature in a magnetic field of 3.3 kG. A positive Overhauser enhancement corresponding to a leakage factor of 0.5 was measured for 14N, showing an important relaxation process due to the hyperfine interaction with electrons. The paramegnetic shift of 14N was measured in a direct way, and the results are in agreement with those of other authors. Overhauser shift measurements were performed for 14N and H; an experimental proof of a negative spin density at the proton was thus obtained.