# Selection Rule¶

## Selection Rule¶

In physics and chemistry, a selection rule, or transition rule, formally constrains the possible transitions of a system from one quantum state to another. Selection rules have been derived for electromagnetic transitions in molecules, in atoms, in atomic nuclei, and so on.

$$\large \Delta l = \pm 1 \quad (\Delta l = 0 \text{ is not allowed.})$$$$\large \Delta m = 0, \pm 1$$
• GRE Physics GR0177 Problem 084