Lin Yen-Cheng, Fidler Ashley P, Sandhu Arvinder, Lucchese Robert R, McCurdy C William, Leone Stephen R, Neumark Daniel M
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Department of Physics, University of Arizona, Tucson, Arizona 85721, USA.
Faraday Discuss. 2021 May 27;228(0):537-554. doi: 10.1039/d0fd00113a.
Multiple Rydberg series converging to the O2+c4Σ-u state, accessed by 20-25 eV extreme ultraviolet (XUV) light, serve as important model systems for the competition between nuclear dissociation and electronic autoionization. The dynamics of the lowest member of these series, the 3sσg state around 21 eV, has been challenging to study owing to its ultra-short lifetime (<10 fs). Here, we apply transient wave-mixing spectroscopy with an attosecond XUV pulse to investigate the decay dynamics of this electronic state. Lifetimes of 5.8 ± 0.5 fs and 4.5 ± 0.7 fs at 95% confidence intervals are obtained for v = 0 and v = 1 vibrational levels of the 3s Rydberg state, respectively. A theoretical treatment of predissociation and electronic autoionization finds that these lifetimes are dominated by electronic autoionization. The strong dependence of the electronic autoionization rate on the internuclear distance because of two ionic decay channels that cross the 3s Rydberg state results in the different lifetimes of the two vibrational levels. The calculated lifetimes are highly sensitive to the location of the 3s potential with respect to the decay channels; by slight adjustment of the location, values of 6.2 and 5.0 fs are obtained computationally for the v = 0 and v = 1 levels, respectively, in good agreement with experiment. Overall, an intriguing picture of the coupled nuclear-electronic dynamics is revealed by attosecond XUV wave-mixing spectroscopy, indicating that the decay dynamics are not a simple competition between isolated autoionization and predissociation processes.
多个里德堡系列汇聚到O2 + c4Σ - u态，通过20 - 25电子伏特的极紫外（XUV）光可访问该态，它们是核解离与电子自电离竞争的重要模型系统。这些系列中最低成员，即21电子伏特左右的3sσg态，由于其超短寿命（<10飞秒），研究其动力学颇具挑战。在此，我们应用阿秒XUV脉冲的瞬态波混频光谱来研究该电子态的衰变动力学。对于3s里德堡态的v = 0和v = 1振动态，分别在95%置信区间内获得了5.8±0.5飞秒和4.5±0.7飞秒的寿命。对预解离和电子自电离的理论处理表明，这些寿命主要由电子自电离主导。由于两个离子衰变通道穿过3s里德堡态，电子自电离速率对核间距有强烈依赖性，导致两个振动态的寿命不同。计算得到的寿命对3s势能相对于衰变通道的位置高度敏感；通过略微调整位置，计算得到v = 0和v = 1能级的寿命分别为6.2和5.0飞秒，与实验结果吻合良好。总体而言，阿秒XUV波混频光谱揭示了一幅引人入胜的核 - 电子耦合动力学图景，表明衰变动力学并非孤立的自电离和预解离过程之间的简单竞争。
