A distribution of the electrons of an atom or a molecular entity over a set of one-electron wavefunctions called orbitals, according to the Pauli principle. From one configuration several states with different multiplicities may result. For example, the ground electronic configuration of the oxygen molecule (
O2) is: 1σg2, 1σu2, 2σg2, 2σu2, 1πu4, 3σg2, 1πg2 resulting in the 3Σg, Δg1 and Σg + 1 multiplets.
Sources:
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1099 (https://doi.org/10.1351/pac199466051077)
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2233 (https://doi.org/10.1351/pac199668122223)