ABSTRACT

The concept of a transition is the basis of spectroscopy. It is the observable associated with a jump from one energy level to another in a quantum mechanical system. In NMR, this is often viewed as the flip of a spin with quantized energy levels in a magnetic field. This is perhaps acceptable for simple systems, but for situations with strong scalar couplings, or dynamics, it is not sufficient. This paper explores some of the many concepts of a transition. In particular, it shows the validity and power of the idea of magnetization being flipped into the xy plane, precessing at its natural frequency, then being detected. This remains true, even in complex systems.