Relativistic ab initio treatment of the second-order spin-orbit splitting of the a (3)Sigma(+)(u) potential of rubidium and cesium dimers - art. no. 012517

We have calculated the splitting between the 0(u)(-) and 1(u) components of the a (3)Sigma (+)(u) state of Rb-2 and CS2 using a relativistic ab initio configuration-interaction valence bond method. This so-called second-order spin-orbit splitting is entirely due to relativistic correlations within t he molecule. Our nb initio nonperturbative splitting is 5 and 3 times large r than perturbative splittings at the inner turning point of the a (3)Sigma (+)(u) potential for Rb-2 and Cs-2, respectively. In addition, close-coupl ed nuclear dynamics calculations that estimate the effect of this splitting on experimentally accessible quantities are presented. The splitting affec ts the collisional loss rate of magnetically trapped ultracold Rb and Cs at oms and the spectroscopic determination of the vibrational structure of Rb- 2 and Cs-2 dimers. Agreement with the experimental collisional loss rates o f Ca is found.