Experimental versus theoretical rates for photoassociation and for formation of ultracold molecules

We report on the spectra of the long-range attractive molecular states of the Cs₂ dimer below the dissociation limits 6s + 6p_1/2 and 6s + 6p_3/2 which are accessible by molecular photoassociation of cold Cs atoms. For the states O_u⁺ and O_g^- (6s + 6p_3/2), we have performed trap-loss measurements, which are in good agreement with the theoretical calculations, performed in a perturbative approach. For the O_g^- and 1_u (6s + 6p_3/2) states, we observe, after spontaneous decay of the electronically excited molecules, the formation of translationally cold molecules. A rate of formation of cold molecules of the order of approx. 10⁶ molecules per second is obtained in the case of the state O_g^-.