selection rule

noun

: a rule that states which of all the conceivable changes in the state of a quantized system (atoms, nuclei, or related entities) are physically possible under specified circumstances usually in terms of the possible numerical changes in the quantum numbers that characterize the system compare allowed, forbidden

The Ultimate Dictionary Awaits

Expand your vocabulary and dive deeper into language with Merriam-Webster Unabridged.

1. Expanded definitions
2. Detailed etymologies
3. Advanced search tools
4. All ad-free

Discover what makes Merriam-Webster Unabridged the essential choice for true word lovers.

Start Your Free Trial Now