Formation of cold Cs-2 ground state molecules through photoassociation in the 1(u) pure long-range state

We report on the formation of translationally cold Cs-2 ground state molecu les through photoassociation in the 1(u) attractive molecular state below t he 6s(1/2)+6p(3/2) dissociation limit. The cold molecules are obtained afte r spontaneous decay of photoassociated molecules in a MOT and in a dark SPO T. We also used polarized atoms, in the f = 3, m(f) = +3 Zeeman ground stat e. Purely asymptotic and adiabatic calculations including hyperfine interac tion and rotation are in excellent agreement with observed structures. As e xpected, the 1(u) state is actually a pure long-range state, consisting of paired atoms, uniquely linked by the first terms of the multipole expansion of the electrostatic interaction. A temperature of 20(-5)(+15) mu K has be en measured for the molecular cloud.