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 ($\ce{O2}$) is: \(1\sigma _{\rm{g}}^{2}\), \(1\sigma _{\rm{u}}^{2}\), \(2\sigma _{\rm{g}}^{2}\), \(2\sigma _{\rm{u}}^{2}\), \(1\pi _{\rm{u}}^{4}\), \(3\sigma _{\rm{g}}^{2}\), \(1\pi _{\rm{g}}^{2}\) resulting in the \(^{3}\Sigma_{\rm{g}}\), \(^{1}\Delta_{\rm{g}}\) and \(^{1}\Sigma_{\rm{g}}^{+}\) multiplets.