在轨道近似理论中,从原子体系的电子组态求相应所包含的各种谱项~(2s+1)L一般是利用Russell-Saunder偶合方法。对于非等价电子,总轨道角动量L和多重度S都可以通过矢量偶合的三角形规则得到,然后再互相组合成所有可能的谱项。对于等价电子,由于有Pauli原理的限制,某些谱项要消失掉,因此往往先由相应组态列出所有可能的简并态(指不存在电子相互作用时),从具有最大总轨道角动量的态开始分别一一 In the theory of orbit approximation, the various spectral terms ~ (2s + 1) L contained in the electronic structure of the atomic system are generally determined by the Russell-Saunder coupling method. For non-equivalent electrons, the total orbit angular momentum L and the multiplicity S can be obtained by the rules of vector-coupled triangles and then combined with each other into all possible spectral terms. For the equivalent electron, due to Pauli’s principle, certain spectrums disappear. Therefore, it is often necessary to first list all possible degenerate states (when there is no electronic interaction) from the corresponding configuration, The state of angular momentum begins one by one