Abstract: For stable excited states of some diatomic molecules, ωe has been known but not Re. The present paper provides an empirical formula relating ωe and Re, ωe=C, which is different from that give in Ref.[9] where α has been considered as a constant 2. Spectrum data of nearly 60 molecules have been simulated using this ωe～Re relation, the results show that the model is universal and reliable in use. At the same time, the first-excited states a 1Δfor NX(X=F, Cl, Br) molecules using the CIS/6-311＋g(3df)、MCSCF/6-311＋g(3df) and B3LYP/6-311＋g(3df) have been calculated. The analytical potential energy function has been also derived using ab initio calculation and spectrum parameters of experiment.

Key words: NX(X=F, Cl, Br) molecules, Potential energy function, ωe～Re relation