Rotational cooling of Li₂(¹Σ_g ⁺) molecules by ultracold collisions with a helium gas buffer

The very weak interaction of Li₂ with He atoms has been obtained from accurate ab initio calculations and is here analyzed in terms of its anisotropic features. Quantum scattering calculations of the rotational inelastic de-excitation cross sections are carried out using a recently proposed multichannel treatment, the modified variable phase method, implemented by the authors and applied here to ultralow collision energies. General conclusions on the low efficiency of a He buffer gas in cooling down molecular rotations in this system are presented and analyzed.