Level-Crossing Signal Line Shapes and Ordering of Energy Levels

Theory and experiments are presented to show that, when correctly interpreted, the sign of the dispersion-shaped term which describes a part of the change in resonance scattering at level crossings can be used to determine the energy ordering of the crossing levels, and hence, in some cases, to obtain the sign of the nuclear magnetic moment. Because of a discrepancy in the literature in the theoretical prediction for the sign of the dispersion-shaped term, we have made a recalculation. The result is borne out by our experiments.