Experimental determination of rotational constants of low-lying vibrational levels in the 0g− pure long-range state of ultracold Cs2 molecule

- High resolution measurements of rotational constants of v=0-3 vibrational levels in pure long range state of ultracold Cs2.
- Double photoassociation spectroscopic method is well utilized to promote the detection sensitivity.
- Binding energies of the rotational levels have been corrected and updated. Good agreement of theoretical value with experimental measurements.

We report an accurate experimental determination of rotational constants of the lowest vibrational levels in the purely long-range state of ultracold cesium molecules (Cs2). We engineer a precise reference of the frequency difference through double photoassociation spectroscopy (PAS). The PAS for the lowest vibrational levels, v=0-3, has been obtained with an enhanced sensitivity and accuracy, according to which the binding energies have been corrected. As deduced from the reference, the frequency intervals between neighboring rotational levels are fitted to a non-rigid rotor model, thus the rotational constants are precisely obtained. The experimental results show good agreement with theoretical expectations.