The A-X electronic transition spectra of halogen diatomic molecules have been measured to
determine the molecular constants and the parameters of potential energy by various 
researchers.
In 2015, we reported a new nonlinear direct potential fitting (DPF) analysis 
that uses “robust” nonlinear least-squares fits to
average properly over the effect of such fluctuations in order to provide an optimum
delineation of the underlying potential energy curve(s).
In the near dissociation limit, it would be difficult to assign the spectra, because in
that area, too dense spectra would be observed. By adopting Stark spectroscopy, the relatively 
low J spectra are emphasized
and the high J spectra become smaller as shown in the figure. This makes it easier to assign 
the low J spectra even in dense
regions. This work reports the spectroscopic constants refined and the parameters of potential energy 
curve recalculated.