Lu-Fano plot for interpretation of the photoassociation spectra

Recently, the method of Lu-Fano plots was extended to potentials with general $R^{-n}$ asymptotic behavior. The aim of this paper is to discuss the efficiency of this method for the interpretation of experimental vibrational spectra of long-range diatomic molecules when two channels are coupled. A Lu-Fano analysis is implemented on experimental data for the ${\mathrm{Cs}}_2{0}_u^{+}{(6S+6P}_{1/2,3/2})$ photoassociation spectra below the ${6S+P}_{1/2}$ and ${6S+P}_{3/2}$ dissociation limits. The parameters are fitted on level energies and predissociation widths, giving information about the asymptotic coefficients $C_3$ for both channels and about a coupling parameter which determines the variation of predissociation widths as a function of detuning. This parameter can be extrapolated above the ${6S+P}_{3/2}$ threshold to yield the fine-structure transition cross section between the two channels. The probability for such a transition in a model where hyperfine structure effects are neglected is found to be 0.54.