摘要:
利用三步双色共振激发技术和三步三色孤立实激发技术,系统地研究了铕原子在42250—44510 cm?1能域内的光谱特性,提供了该能域内56个束缚高激发态的光谱信息.为了能确定这些态的光谱归属,进行了两方面的探索:第一,观察能否利用孤立实激发技术,把处于这些态上的铕原子进一步共振激发到自电离态,从而推断这些态属于单电子激发的束缚Rydberg态还是属于双电子激发的价态,并对Rydberg态的电子组态进行了光谱确认;第二,通过计算这些态相对于各个电离阈的量子亏损并观察它们分别收敛于哪个电离阈,以便获取其主量子数的信息.最后,设计并采用了三种不同的激发路径,分别将原子布居到同一高激发能域并探测它们在该能域的光电离光谱.通过比较这些光谱的异同并结合上述激发路径所对应的跃迁选择定则,便可惟一地确定这些高激发态的总角动量.研究发现:所探测到的高激发束缚态只有三个属于单电子激发的束缚Rydberg态,其余都是价态.本文确定了这三个Rydberg态的电子组态和原子状态.
Abstract:
The three-step two-color resonant ionization method and three-step three-color isolated-core excitation (ICE) tech-nique are used to study the spectra of the highly excited bound states systematically, either Eu 4f76snl Rydberg states or other valence states converging to the higher ionization limits. Specifically, the highly excited bound states are populated from the ground state via three different 4f76s6p intermediate states, thereby establishing the three different excitation schemes. The schemes are designed to allow us to assign a J-quantum number uniquely to a given highly excited state with the selection rules of J-quantum number for each excitation scheme by comparing their corresponding photoion-ization spectra, which are obtained with three-step two-color resonant ionization method. By tuning the wavelength of the second laser, the 56 highly excited bound states located in the energy region between 42250 cm?1 and 44510 cm?1 are detected. To explore their spectroscopic information, more efforts have been made 1) to judge whether an excited state is a bound Rydberg state and to observe whether it may be excited further to an autoionizing state by using the ICE technique;2) to deduce the principal quantum number of the given bound Rydberg states, and to observe whether they are converged to the same ionization limit by calculating their quantum defects with respect to several ionization limits. Based on the above manipulations, all detected highly excited bound states can be classified as the two categories:bound Eu 4f76snl Rydberg states and other valence states converging to the higher ionization limits, such as the Eu 4f75dnl states. Specifically, to fulfill the ICE technique, it is necessary to make a resonance transition from the 4f76snl Rydberg states to the 4f76p1/2nl autoionizing states with the third dye laser whose wavelength is scanned around the Eu 4f76s+-4f76p+1/2 ionic line. Once the Eu 4f76snl Rydberg states are recognized with the ICE technique, the identification of their orbital quantum numbers is a primary task to determine their electron configurations. With all the efforts mentioned and existing information, three Rydberg states can be assigned to the 4f76s10s(8So9/2), 4f76s9d(8Do9/2) and 4f76s9d(6Do7/2), whereas the rest can be regarded as highly excited valence states.
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