本實驗利用雙光子共振光譜法(Optical–Optical Double Resonance, OODR)來偵測雙原子鈉分子其對稱(gerade)的高能位單重態。首先使用氬離子雷射將雙原子鈉分子由基態(X1Sg+)激發到B1Pu電子態，再使用Ti-sapphire雷射將雙原子鈉分子由B1Pu電子態激發至欲偵測之上態。雷射激發躍遷方程式如下:
B1Pu(v’, J’) X1Sg+ (v”, J”) + hn1
21Dg(v, J) 或 31Pg(v, J) B1Pu(v’, J’) + hn2
而偵測方法，則是偵測鈉分子從高能位的單重態經由碰撞後到高能位的三重態，再躍遷回a3Σg+電子態的螢光訊號。
本實驗為首次利用實驗之方法偵測到雙原子鈉分子之21Dg電子態，偵測到v＝0~23, 25~28等28個振動能階值，轉動能階分佈在J＝11～99，共計有582個振轉能階。將偵測所得之實驗數據經計算得到一組分子常數，並建立其RKR位能曲線。
實驗中也偵測得到31Pg電子態246個振轉能階，其中包括有27個振動能階值v=0～26，而轉動能階分佈在J＝11～99。將實驗所偵測而得之數據經計算得到一組新的分子常數，並建立RKR位能曲線。

Using the optical-optical double resonance spectroscopy (OODR) technique, two Rydberg electronic states with gerade-parity of Na2 were observed. Na2 molecules were pumped from the X1Sg+ state to the intermediate B1Pu state by an Ar+ laser. Then, the Ti-sapphire laser further excites molecules from the intermediate B1Pu state to the higher excited states. The transitions can be described as:
B1Pu(v’, J’) X1Sg+ (v”, J”) + hn1
21Dg(v, J) or 31Pg(v, J) B1Pu(v’, J’) + hn2
The triplet Rydberg states, such as 23Pg, 33Pg or 3Sg+, were populated via collision energy transfer from 21Dg or 31Pg states. The fluorescence from triplet electronic states to a3Σg+ state was monitored by a filtered- PMT.
The 21Dg state is experimentally observed by OODR method for the first time. We have observed 582 rovibrational levels with the vibrational and rotational quantum in the range of 0≦v≦28 and 11≦J≦99, respectively. The vibrational quamtum nunber assignment was confired by the comparison of excitation intensities and result fluorescence with the calculated Franck-Condon factors (FCF) between the 21Dg and B1Pu states. The Dunham coefficients and RKR potential energy curve were determined in this study.
In the meanwhile, we also observed 246 rovibrational levels, including 27 vibrational levels of the 31Pg state. The Dunham coefficients were determined for higher range of rotational quantum, 11≦J≦99, and the RKR potential energy curve were constructed.

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