configuration (electronic)

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: $1 σ g 2$ , $1 σ u 2$ , $2 σ g 2$ , $2 σ u 2$ , $1 π u 4$ , $3 σ g 2$ , $1 π g 2$ resulting in the $Σ g 3$ , $Δ g 1$ and $Σ g + 1$ multiplets.

Source:

PAC, 1994, 66, 1077 (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1099

PAC, 1996, 68, 2223 (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2233