We analyze ionic spectrum of lanthanum via intermediate state (Xe) 5d6d3F2 in the energy region 89872-91783 cm-1, and the spectrum is obtained using five-laser resonance excitation in combination with a method of sequential ionization by a pulsed electric field and a constant electric field, and has been recalibrate in this work. Both of one strong and one weak autoionization Rydberg series converging to the La2+ state are determined. Meanwhile, the two autoionization Rydberg series are assigned by relativistic multichannel theory (RMCT) within the framework of multi-channel quantum defect theory (MQDT). More specifically, the strong autoionization Rydberg series is assigned to 5dnp(5/2,1/2)3 and/or 5dnp(5/2,1/2)2, and the weak autoionization Rydberg series is assigned to 5dnf (5/2,5/2)3 and/or 5dnf(5/2,5/2)2. We focus on the behavior of quantum defect with excitation energy for high Rydberg states, which are sensitive to the existence of a external field. We find the breakdown of quantum defect regular behavior for a specific Rydberg series and autoionization Rydberg series of La+ as the effective quantum number n*＞67. Due to that our calculations, which are obtained by relativistic multichannel theory and included configuration interactions, are in basically agreement with that for experimental low n (n*＜67) Rydberg states as well as small stray electric fields, we suggest that plasma formed by photoionization of La atoms in the second excitation step may be responsible for the breakdown of quantum defect regular behavior.%基于五步激光共振激发, 经由中间态(Xe)5d6d 3F2的一价镧离子光谱, 分析了该实验谱, 确定了一价镧离子一强一弱两个自电离里德伯系列. 同时利用多通道量子亏损理论(MQDT) 框架下的相对论多通道理论(RMCT) 计算, 标识了这两个自电离里德伯系列, 强的自电离里德伯系列标识为5dnp(5/2,1/2)3和/或5dnp(5/2,1/2)2, 弱系列标识为为5dnf(5/2,5/2)3和/或5dnf(5/2,5/2)2.根据实验谱峰数据, 发现有效量子数很高时, 里德伯和自电离里德伯能级量子数亏损随激发能量不平滑变化, 并分析了可能的原因.
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