Resonant coupling in the formation of ultracold ground state molecules via photoassociation

We demonstrate the existence of a new mechanism for the formation of ultracold molecules via photoassociation of cold cesium atoms. The experimental results, interpreted with numerical calculations, suggest that a resonant coupling between vibrational levels of the 0(u)(+) (6s + 6(P1/2)) and (6s + 6p(3/2)) states enables formation of ultracold molecules in vibrational levels of the ground state well below the 6s +f 6s dissociation limit. Such a scheme should be observable with many other electronic states and atomic species.