Selection rule

{
  "id": "MLC-T-CHM-010672",
  "term": "Selection rule",
  "field": "Chemistry",
  "definition": "A rule, derived from the symmetry and spin of the initial and final wavefunctions, that states whether a transition between two quantum states is allowed or forbidden. In electronic spectroscopy the spin rule requires the spin multiplicity to stay unchanged, so singlet to triplet absorption is spin-forbidden, and the Laporte rule forbids transitions between states of the same parity in centrosymmetric molecules. Spin-forbidden bands have molar absorption coefficients orders of magnitude smaller than those of allowed bands.",
  "subject": "Organic and Biomolecular Chemistry",
  "references": [
    "PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2273 (https://doi.org/10.1351/pac199668122223)"
  ],
  "url": "https://mlchart.com/terminology/chemistry/selection-rule/"
}