For modelling the line intensities of the low-overtone bands ($\Delta v\le 3$ in CO), any potential-energy and dipole-moment functions (PEFs and DMFs) that describe the available data can be used. This is not true for the high-overtone bands. The Born-Oppenheimer molecular functions as functions of the interatomic separation $r$ must obey some restrictions in the complex plane of $r$. In particular, the PEF and DMF must have common singularities in the complex plane and the DMF should not rapidly increase upon displacement from the real axis. Two model DMFs are considered for CO, a fully regular function over the entire complex plane and an irregular one with two branch points corresponding to complex intersections of the ground-state PEF with the excited-states ones. The predictions of the 7-0 band made with the regular DMF turn out to be unstable with respect to small variations in the database, which is associated with very rapid variations of this DMF. On the contrary, the predictions of the irregular one are stable and therefore are considered to be more reliable.

用于模拟低泛音带的线强度（$\Delta v\le 3$在 CO）中，可以使用描述可用数据的任何势能和偶极矩函数（PEF 和 DMF）。对于高泛音频段而言，情况并非如此。Born-Oppenheimer 分子作为原子间分离的函数$r$ 必须遵守复杂平面中的一些限制 $r$. 特别是，PEF 和 DMF 必须在复平面中具有共同的奇点，并且 DMF 不应在从实轴位移时迅速增加。CO 考虑了两种模型 DMF，一种是在整个复平面上的完全规则函数，另一种是具有两个分支点的不规则函数，对应于基态 PEF 与激发态 PEF 的复杂交叉点。使用常规 DMF 对 7-0 波段的预测结果在数据库中的小变化方面不稳定，这与此 DMF 的快速变化有关。相反，不规则的预测是稳定的，因此被认为更可靠。