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 Cs₂0_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 C₃ 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.