Theoretical treatment of channel mixing in excited Rb2 and Cs2 ultracold molecules:: Perturbations in 0u+ photoassociation and fluorescence spectra -: art. no. 022504

The mapped Fourier grid method, using a coordinate adapted to the local de Broglie wavelength associated to the vibrational motion in a molecule, and recently developed by Kokoouline et al. [J. Chem. Phys. 110, 9865 (1999)], is used to compute the perturbed binding energies and rotational constants of the Cs-2 0(u)(+) (6s + 6p P-2(1/2,3/2)) photoassociation spectrum below the lower dissociation limit. The results are shown to be very sensitive to the molecular potential curves and spin-orbit coupling. In the case of Rb-2 0(u)(+) (5s + 5p P-2(1/2,3/2)), a strong isotopic effect is also predicted. The results can be interpreted in the framework of generalized two-channel quantum defect theory, and generalized Lu-Fano plots are presented. This work suggests that parameters could easily be fitted to experimental spectra, eliminating the difficulties caused by limitations in the accuracy of the short-range molecular potentials.