Highly sensitive photoassociation spectroscopy of ultracold 23Na133Cs molecular long-range states below the 3S1/2＋6P3/2 limit

We present high resolution photoassociation spectroscopy of ultracold 23Na133Cs molecules in a long-range c3∑＋ state below the （3S1/2 ＋ 6P3/2） asymptote. We perform photoassociation spectroscopy in a dual-species magneto-optical trap （MOT） and detect the photoassociation resonances using trap-loss spectroscopy. By fitting the experimental data with the semi-classical LeRoy-Bernstein formula, we deduce the long-range molecular coefficient C6 and derive the empirical potential energy curve in the long-range region.