Spin effects in (6 s1/2 +6 p1/2) 0u+ Cs2133 weakly bound molecules analyzed by using the Lu-Fano method coupled to the improved LeRoy-Bernstein formula

We present an analysis of spectroscopic data concerning the long-range molecular state (6 s1/2 +6 p1/2) 0u+ of Cs2133 by using the Lu-Fano method coupled to the improved LeRoy-Bernstein formula. The obtained Lu-Fano graph exhibits the coupling of molecular series to the (6 s1/2 +6 p3/2) 0u+ state. The coupling is due to the spin effects in the molecule. A two-channel model involving the improved LeRoy-Bernstein formula allows us to characterize the molecular series, to localize the perturbing levels, to evaluate the coupling in the vicinity of each perturbing level (five observed for Cs) in a two-level approach and in a more accurate multilevel description. Furthermore, we predict the energy and the width of the first predissociated level. © 2008 The American Physical Society.