本文从双原子分子的电子角动量出发,介绍了如何由电子组态确定其光谱项。较为详尽的讨论了如何确定谱项关于凭借包含键轴的平面的反映操作的对称性,即用+、-表示的对称性。对于同核双原子分子,还讨论了如何确定谱项关于凭借分子中心的反演操作的对称性,即用g、u表示的对称性。 Starting from the electronic angular momentum of diatomic molecules, this paper describes how to determine the spectral items from the electronic configuration. More detailed discussion is given on how to determine the symmetry of a spectral term with respect to the plane of reflection that contains the key axis, ie, +, -. For homonuclear diatomic molecules, we also discuss how to determine the symmetry of the spectral terms with respect to the inversion operation by virtue of the molecular centers, that is, the symmetry expressed by g, u.