Highly excited states of ultracold molecules: Photoassociative spectroscopy of Na-2

We describe the spectroscopy of highly excited states of ultracold Na-2 mol ecules using a neu photoassociative approach based on resonantly enhanced m ultiphoton ionization; We excite a remarkable number of Na-2 rotational sta tes providing a rich rovibrational spectrum. We thereby extract not only th e first order quadrupole-quadrupole (C-5) and the van der Waals constants ( C-6) but also sensitive atom-atom interaction parameters such as spin-spin, spin-orbit, and perturbative constants.