hyperfine (interaction)

https://doi.org/10.1351/goldbook.HT07394
Interaction between the electron spin S and the nuclear spin I.
Source:
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 353 (https://doi.org/10.1351/pac200779030293)