【作者】 林梅；

【导师】 朱林繁；

【作者基本信息】 中国科学技术大学 ， 原子与分子物理学， 2013， 博士

【摘要】 本论文在研制基于快电子能量损失谱仪的电子-离子符合测量装置的基础上,研究了氧气分子和笑气分子超激发态在不同动量转移下的退激发行为。在实验装置发展方面,我们在原有的角分辨快电子能量损失谱仪的基础上,设计并安装调试了正离子飞行时间质谱仪,建成了快电子能量损失符合谱仪,并改进了原有的数据处理方法,实现了用离子飞行时间质谱测量部分离子碎片的振子强度密度。在物理工作方面,我们测量了氧分子和笑气分子超激发态在不同动量转移下的退激发通道。在氧分子超激发态的退激发研究中,观测到了大动量转移下一些超激发态的退激发信息,首次给出了收敛到c4∑。-的光学禁戒的里德堡态的退激发行为。在笑气分子的研究中,测量了其超激发态在不同动量转移下的退激发通道。我们的实验结果表明,在散射角度0°和2°条件下,笑气分子超激发态通过中性成份退激发和电离成份退激发的强度比随动量转移而呈现出明显的变化,这与以往大家认为的超激发态的制备和演化是两步过程的假设不一致,我们结合Fano关于束缚态和连续态的相互作用理论给出了初步的分析。在第一章中,介绍了超激发态的基本概念和主要的研究方法。我们根据采用的符合测量方法以及探测到的次级粒子种类的不同,对实验方法进行了分类。随后介绍了目前国际上研究超激发态的主要实验手段以及各自测量得到的物理量。通过比较,明确了不同实验手段可以给出的物理信息。在第二章中,介绍了快电子能量损失谱方法和电子-离子符合测量方法的原理。重点介绍了微分截面、光学振子强度和广义振子强度的物理概念,以及本工作中使用的绝对标定方法。另外,简单介绍了电子-离子符合法测量特定碎片离子的部分振子强度密度的原理。最后,我们从群论的角度对分子跃迁定则进行了推导。在第三章中,具体介绍了我们的电子-离子符合快电子能量损失谱仪的设计原理及符合系统的安装调试、数据处理和初步结果。在第四章中,我们利用快电子能量损失符合谱仪,在入射电子能量2500eV的条件下,测量了散射角度为0°、2°和4°的氧分子超激发态和电离连续区的电子能量损失谱及部分离子碎片的振子强度密度谱,首次研究了氧分子收敛于c4∑u-的光学禁戒的里德堡态的退激发通道对动量转移的依赖行为。在第五章中,利用电子-离子符合方法,在2500eV入射电子能量条件下,测量了散射角度为0°和2°、能量范围为12eV-22eV的超激发态的电子能量损失谱和部分离子碎片的振子强度密度谱,并对13.8eV和14.0eV处的两个峰进行重新标识,给出了收敛到Az∑+和C2∑+的超激发态在不同角度的退激发通道。我们的实验结果显示出,在散射角度0°和2°条件下,笑气分子超激发态通过中性成份退激发和电离成份退激发的强度比随动量转移而呈现出明显的变化,这与以往大家认为的超激发态的制备和演化是两步过程的假设不一致,我们结合Fano关于束缚态和连续态的相互作用理论做出了初步的分析。更多还原

【Abstract】 In this dissertation, the method of electron-ion coincidence was used to study the momentum transfer dependence behaviors of decay pathways of superexcited states and structured ionization region of oxygen and nitrous oxide. In the respect of experimental setup development, the time of flight mass spectrometer (TOFMS) was installed and fully tested as a part of the Electron Energy Loss Coincidence Spectrometer. A modified data acquisition system controlled by computer was developed to record the collision events of positive ions so that the decay information from the ionization continuum or discrete superexcited states to different channels of ionic fragments can be detected by measuring the scattered electrons and ions coincidently. Then the decay pathways of superexcited states of oxygen and nitrous oxide at different momentum transfers were measured. The dipole-forbidden superexcited states of oxygen were observed, and their decay pathways at different momentum transfers were measured. It is found that the dipole-forbidden superexcited states of (2σu)-1(c4∑u-)npσu3∑8-←X3∑8-decay into different channels according to the principal quantum number n. As for nitrous oxide, we measured the decay pathways of superexcited states of nitrous oxide at the scattering angles of0°and2°. Our results show that the intensity ratio of neutral dissociation channel and ionization channel varies with the momentum transfer, which conflicts with the traditional assumption that the preparation and the evolution of the superexcited state is a two-step processes although it has not been verfied experimentally. Combining Fano’s theory about interaction between the discrete state and the continuum, we give a preliminary analysis.In chapter1, the concept of superexcited state and the major experimental methods were introduced. According to the coincidence method, different experimental methods were categorized. The main experimental methods and the detemined physical information were introduced and compared. In chapter2, we give a brief review about the concepts of the differential cross section, the optical oscillator strength, the generalized oscillator strength and the absolute calibration method. Moreover, the coincidence method of measuring the partial generalized oscillator strength density of the specific fragment ions was also described. Finally, we carried out the theoretical derivation of the transition rule of linear heternuclear molecules from the perspective of group theory.In chapter3, the design principle of electron-ion coincidence fast electron energy loss spectrometer was introduced. The process of installing and commissioning of the system, as well as the data processing method and the preliminary results were described.In chapter4, the electron energy loss spectra and the partial generalized oscillator strength density (GOSD) of structured ionization region of oxygen at different momentum transfers, i. e.,0,0.23, and0.91a.u., were studied by the electron-ion coincidence fast electron energy loss spectrometer at an incident electron energy of2.5keV. Besides the dipole-allowed superexcited states, the dipole-forbidden Rydberg series converging to c4∑u-were observed, and it was the first time that their decay pathways at different momentum transfers were measured.In chapter5, the electron energy loss spectra, the ionization GOSD, as well as the partial GOSD, of the structured ionization region12-22eV of nitrous oxide at the scattering angles of0°and2°were studied by measuring the ion and the scattered electron coincidently at an incident electron energy of2.5keV. The two transitions at13.8eV and14.0eV were reassigned. The decay pathways of the superexcited states converging to A2∑+and C2∑+at different momentum transfers were measured. Our results revealed that the ratio of the intensities of neutral dissociation channel and ionization channel shows varies with the momentum transfer, which conflicts with the prevalent assumption that the preparation and the evolution of superexcited state is a two-step processes.Combining Fano’s theory about interaction between the discrete state and the continuum, the preliminary analysis was given.更多还原