用速度影像法研究Eu原子4f^76p_(1/2)8s自电离态的弹射电子角分布

Angular Distribution of Ejected Electrons from Eu 4f^76p_(1/2)8s Auto-Ionizing State Studied by Velocity Mapping Imaging Technique

采用速度影像技术研究了Eu原子4f76p1/28s自电离态的弹射电子角分布,能量覆盖了60600.0~61860.2cm-1的范围。实验采用三步孤立实激发方法分步从基态4f76s28S7/2经中间态4f76s6p 6P5/2激发到4f76s8s8S7/2Rydberg态上,然后将其进一步共振激发至4f76p1/2(J=3)8s和4f76p1/2(J=4)8s自电离态。根据所用的激发路径及其选择定则可以得出自电离态的总角动量的可能取值;通过自电离过程的能量守恒,角动量守恒和宇称守恒原理推测出其向不同离子终态衰变所对应的弹射电子的能量范围和特性。利用电子透镜对上述自电离过程中产生的弹射电子进行聚焦和成像,通过位置敏感探测器对其动能进行分辨,运用速度影像技术进行数学变换和计算得到弹射电子的角向分布。同时,通过调谐第三步激光的波长,得出了角分布和各向异性参数随光子能量的变化规律,并给出了相应的物理解释。

The angular distribution of the electron ejected from Eu atom 4f76p1/28s auto-ionizing state, whose energy range covers from 60600.0 cm-1 to 61860.2cm-1, has been investigated in use of the velocity mapping imaging technique. Eu atom is stepwise excited from the 4f76s28 S7/2 ground state to the 4f76s8s 8 S7/2 Rydberg state through the 4f76s6p 6 Ps/2 intermediate state, then excited to the 4f76p1/2 （J = 3） 8s and 4f 6p1/2 （J = 4） 8s auto-ionizing states further by using the three steps isolated-core-excitation method. The value of the total angular momentum is calculated by the excitation scheme and the selection rule, the energy range and properties are deduced from the energy, angular momentum and parity conservation in auto-ionization process. The ejected electron, which is the production of the auto-ionization process, is focused and imaged by the electron lens. The kinetic energy of it is resolved by the position sensitive detector, and by using the velocity mapping imaging technique, mathematical transformation and calculation for ejected electron angular distribution is carried out. Simultaneously, by tuning the wavelength of the third dye laser, the propensity of the angular distribution and the anisotropy parameters following the variation of the photon energy has been obtained, and the physical essence has been discussed.