利用一步激光共振激发精密测量镧锕系元素第一电离势

The first ionization potential (IP) is a fundamental physical and chemical property of an element. Precision measurement IP is important for identifying systematic trends in binding energies from element to element and for drawing conclusions about the electronic structure of an atom as the first IP is directly connected to the atomic spectra. Up to now, it is still hard to accurate calculate the IPs of the heavy elements especially for the elements with more than one open shells outside a closed electron core. The traditional multi-step resonant excitition technique is the widest used method to measure the IPs of most elements. However, the precision of IPs for the heavy elements measured by multi-step resonant excitition are relative lower than that for the light elements because that the complex electronic structure of heavy element. The project proposes one-step resonant excitation technique as a new method to measure the IPs of heavy elements, which will avoid the intermediate state and extremely simplifies the experimental process. The new method will be a useful tool for atomic structure research and the identification of super-heavy elements. The deep UV pulsed laser employed in this project is specially designed to be tunable in 195-210 nm range with the narrowest bandwidth as a pulsed laser in the world. Four elements Ho, Er, Th and U from the lanthanides and actinides will be measured in our project and the feasibility and reliability of the new method will be verified. The accurate experimental values of heavy atomic IPs will be helpful for testing the theoretical model of the electronic structure of heavy atoms and extending it to the super-heavy elements.

电离势是确定元素物理属性与化学行为的最基本的物理量。由于电离势与原子光谱直接相关，因此，精密测量元素电离势对于我们理解元素原子结构及其系统性变化规律的非常重要。目前，理论精确计算镧锕系等具有多个开放电子壳层的重元素电离势难度很大，而传统的多步激光共振激发技术已经测量的镧锕系元素电离势精度较低。为此，本申请提出了基于一步激光共振激发技术精密测量重元素电离势的新方法，这种方法在国际上尚无实验报道。本项目计划通过对Ho、Er、Th、U四种镧锕系元素高里德堡能级的实验研究，验证一步激光共振激发技术测量元素电离势的可行性。由于避免了使用中间能级，并且激光器线宽较国际同行压缩了一个量级以上，因此本项目有望提高其中1~2种元素电离势的测量精度，为检验重元素的理论计算模型提供实验数据。此外，一步激光共振激发技术也将为结构信息尚不清楚超重元素激光谱学鉴别、新核素电离势测量及其结构研究提供新方法

电离势是确定元素物理属性与化学行为的最基本的量，它与原子光谱直接相关。精密测量元素电离势对于我们理解元素原子结构及其系统性变化规律的非常重要。目前，理论精确计算镧锕系等具有多个开放电子壳层的重元素电子结构难度很大，而传统的多步激光共振激发技术已经测量的镧锕系元素电离势精度较低。为此，本项目提出了探索利用一步激光共振激发技术精密测量重元素电离势的新方法。.项目首先针对镧锕系测量需求进行了实验装置改进，包括提高电子枪高温原子炉坩埚的工作寿命；提高腔室真空度以降低背景信号干扰；发展了基于PXIe新型激光共振电离质谱技术的数据采集系统。在此基础上，开展了U元素的三步激光共振激发光电离谱测量，获得了U元素第一电离势为49946.13cm-1；利用极窄线宽深紫外激光开展了U元素的一步共振激发光电离谱，验证一步激光共振激发技术测量元素电离势的实验可行性，并获得了高分辨U元素高里德堡能级光谱数据。针对一步共振激发光电离谱能级归属的困难，我们尝试利用外电场下一步激光共振激发电离阈测量的方法进行U元素第一电离势，目前已完成了基于外电场下电离阈发测量元素电离势的测试实验。针对镧锕系元素已发表的光谱数据非常有限的问题，我们在实验上还测量了U、Th、Ho三种元素的高分辨发射光谱，为共振电离光谱分析提供参考和数据。.综上，本项目验证了利用一步激光共振激发测量元素第一电离势实验的可行性，完成了U元素的一步共振激发光电离谱的测量工作。所得到的光谱数据及数据分析方法等可为结构信息尚不清楚超重元素激光谱学鉴别、新核素电离势测量以及核燃料生产等提供参考。