Observation of the NaD C1$\Sigma +$ state near the region of dissociation limit*

Using pulsed optical-optical double resonance fluorescence depletion spectroscopy, we observed the C1$\Sigma +$ state levels of gaseous sodium deuteride molecules. In this work, total of 369 rovibrational levels were recorded including vibrational quantum numbers from 10 to 58 and rotational quantum numbers from 3 to 10. The avoid-crossing of shallow-dish well in the inner potential energy curve causes the irregular behaviors of Bv and $\Delta $Gv near the dissociation limit. A comparison of molecular properties between NaH and NaD will be presented.