Photoassociation spectra of ultracold ⁸⁵Rb₂ molecule in 0_u⁺ long range state near the 5S_1/2+5P_1/2 asymptote

We investigate the high resolution photoassociation spectra of ⁸⁵Rb₂ molecules in 0_u⁺ long range state below the (5S_1/2 + 5P_1/2) asymptote. The ⁸⁵Rb atomic samples are trapped in a dark magneto-optical trap (MOT) and prepared in the dark state. With the help of trap loss technique, we obtain considerable photoassociation spectroscopy with rovibrational resolution, some of which have never been observed before. The observed spectrum is fitted by a rigid rotation model, and the rotational constants of ultracold ⁸⁵Rb₂ molecule in long range 0_u⁺ are obtained for different vibrational states. By applying the LeRoy-Bernstein method, we assign the vibrational quantum numbers and derive C₃ coefficient, which is used to obtain the potential energy curve.