Rotational cooling of Li-2((1)Sigma(+)(g)) molecules by ultracold collisions with a helium gas buffer

The very weak interaction of Li-2 with He atoms has been obtained from accurate ab initio calculations and is here analyzed in terms of its anisotr opic features. Quantum scattering calculations of the rotational inelastic de-excitation cross sections are carried out using a recently proposed multichan nel treatment, the modified variable phase method, implemented by the authors and applied here to ultralow collision energies. General conclusions on the l ow efficiency of a He buffer gas in cooling down molecular rotations in this system are presented and analyzed