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g (gerade) 對稱的高能位單重態(singlet state)。首先使用氬離子雷射將雙原子鈉分子由基態(X1Σg+)激發到B1Πu電子態，再使用染料雷射(R6G)將雙原子鈉分子由B1Πu電子態激發至欲偵測之上態。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a3Σu+電子態的螢光訊號。

　　實驗中，共偵測得到6d1Δg電子態88個振轉能階，其中包括43個e-level和45個f-level，振動能階值v=0～11，而轉動能階分佈在J＝11～83。7d1Δg電子態79個振轉能階，其中包括51個e-level和28個f-level，振動能階值v=0～10，而轉動能階分佈在J＝11～83。8d1Δg電子態49個振轉能階，其中包括30個e-level和19個f -level，振動能階值v=0～10，而轉動能階分佈在J＝11～65。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。

　　分析L-耦合分離的部分，6d1Δg電子態的L-偶合分離現象隨著振動和轉動量子數的增加有變明顯的趨勢，7d1Δg電子態L-耦合分離的現象隨著振動量子數的增加有變明顯的趨勢，但在看和轉動量子數的關係時無法判斷其趨勢。8d1Δg電子態L-耦合分離的現象隨著轉動量子數的增加有變明顯的趨勢，但在看和振動量子數的關係時無法判斷其趨勢。

　　Using optical-optical double resonance spectroscopy (OODR), three singlet Rydberg electronic states with gerade-symmetry of Na2 have been observed. Na2 molecules were pumped from the X1Σg+ state to the intermediate B1Πu state by a single line Ar+ laser. Then, the ring dye laser(operated with R6G dye) further probed molecules from the intermediate B1Πu state to the higher excited states. The transitions can be described as:
B1Πu(v’, J’) ← X1Σg+ (v”, J”) + hν1
nd1∆g(n=6,7,8) ← B1Πu(v’, J’) + hν2
　
　Some triplet Rydberg states were populated from the singlet states probed via collision energy transfer. The violet fluorescence from those triplet electronic states to a3Σu+ state was monitored by a filtered- PMT.

　We have observed 88 rovibrational levels in the 6d1Δg state, which includes 43 e-levels and 45 f-levels with the vibrational and rotational quantum in the range of 0≦v≦11 and 11≦J≦83, respectively. We have observed 79 rovibrational levels in the 7d1Δg state, which includes 51 e-levels and 28 f-levels with the vibrational and rotational quantum in the range of 0≦v≦10 and 11≦J≦83, respectively. We have observed 49 rovibrational levels in the 8d1Δg state, which includes 30 e-levels and 19 f-levels with the vibrational and rotational quantum in the range of 0≦v≦10 and 11≦J≦65, respectively. The Dunham coefficients with Λ-doubling constants and RKR potential energy curve were determined for these states (nd1Δg n=6,7,8).

　In this study, the splitting of Λ-doubling in these states could be measured under our experimental resolution. This splitting is due to the Hund's coupling transition from case (a) to case (d) and should be increased as increasing the principal quantum number n.

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