Grimm–Sommerfeld rule

The Grimm–Sommerfeld rule is a principle used in quantum mechanics that helps to estimate the transition rates between quantum states, particularly in the context of atomic and molecular transitions. It provides a way to understand the selection rules governing the allowed or forbidden transitions between different energy levels of a quantum system. The rule was formulated by the physicists Wilhelm Grimm and Arnold Sommerfeld, and it applies primarily to electric dipole transitions.