An Etymological Dictionary of Astronomy and Astrophysics

A → selection rule obeyed by → discrete transitions. Among them are: rigorous selection rules for → electric dipole transitions (→ permitted) requiring:

1. ΔJ must be 0 or ± 1 with J = 0 ↔ 0 forbidden.
2. ΔM_J = 0, ± 1.
3. → Parity change, i.e. even ↔ odd.

See also: → rigorous; → selection; → rule.