Photoassociation of ultracold RbCs molecules into the （2）0- state （v = 189,190） below the 5S1/2 ＋ 6P1/2 dissociation limit

Ultracold polar RbCs molecules are produced via photoassociation in a laser-cooled mixture of 85Rb and 133Cs atoms. The a 3Σ+ state molecules which decay from electronically excited (2)0- state RbCs molecules are detected by resonance-enhanced two-photon ionization. The new rovibrational levels (v = 189, 190) in the (2)0- state are also observed, which exist in theory and have not been observed in experiments yet. The corresponding rotational constants are measured by photoassociation spectroscopy, which are consistent with theoretical calculations using a nonrigid rotor model.