原子分子激发动力学的高分辨X射线散射研究

发布时间：2018-03-04 19:38

本文选题：X射线散射　切入点：原子分子　出处：《中国科学技术大学》2016年博士论文　论文类型：学位论文

【摘要】：原子与分子物理,始终是物理领域的重要组成部分。对单个原子分子结构的认识,形成了等离子体物理、凝聚态物理、天体物理等物理学科乃至化学、材料学、生物学等其它领域研究的基础。原子分子的特性主要包含两个方面：能级结构和对应的位置空间或动量空间电子结构。其中后者的实验探索主要是基于散射过程的动力学参数,常以振子强度或者形状因子(跃迁矩阵元)平方来表示,可以直接反映出电子波函数的分布信息。如今原子分子能级结构的测量已经达到了极高的精度(10.16),但动力学参数的测量精度却往往只有百分之几到百分之几十,普遍意义上的高精度测量也存在5%左右的误差,且直至今日对散射过程背后的物理机制仍存在许多不确定性或争议。因此,发展一种全新的散射实验方法,获得较精准的动力学参数实验基准数据,理解各种研究方法的利弊并探究其散射机理,就显得十分重要。目前,研究原子分子振子强度或形状因子平方的主要实验方法有光吸收方法、高能电子散射方法和X射线散射方法。其中,光吸收方法可以测量动量转移接近零时原子分子的光学振子强度。高能电子散射和X射线散射方法既可以用来测量偶极允许跃迁的光学振子强度,也可以用来获得偶极允许和偶极禁戒跃迁的动量转移依赖的动力学参数。光吸收方法和高能电子散射方法很早就用于原子分子动力学参数的测量,获得了大量的实验基准数据。高分辨X射线散射方法则不同,它是最近(2009年)才被本研究组引入原子分子领域的,且作为一种新的方法,一方面可以揭示新的原子分子碰撞机理,另一方面可以交叉检验已有的实验基准,因而有着广阔的应用前景。本论文的主要内容就是在进一步发展高分辨X射线散射技术的基础上,开展原子分子的光学振子强度、弹性和非弹性形状因子平方的系统研究。具体内容为：1、以非弹性X射线散射方法获得了氩原子、氢分子和氮分子价壳层激发形状因子平方的实验基准数据,其中首次从实验上给出了氢分子和氮分子电子振动激发态的形状因子平方。所有这些测量结果与最近的理论计算均符合很好。通过对比X射线散射实验和高能电子散射实验得到的动力学参数,发现对多电子体系而言,在高能电子散射过程中往往存在着明显的分子内散射,一阶玻恩近似很难成立。还有,一般人们认为,高能电子散射实验在不同入射电子能量下所得动力学参数趋于一致,可以作为一阶玻恩近似成立的判据,但我们的实验结果清楚地表明这一判据并不严格成立,高阶玻恩项也显示出和入射电子能量无关的特性；2、首次提出并实现了测量光学振子强度的dipole(γ,γ)方法。光吸收过程中光子把自身所携带的所有能量和全部动量都传递给了原子分子,其特点是能量传递较大(eV量级),而动量转移极小(10-3a.u.)。我们提出利用小角度(2。)X射线散射过程中动量转移极小的特点模拟光吸收过程,进而可用它测量原子分子的光吸收截面,我们命名它为dipole(γ,γ)方法。本论文利用dipole(γ,γ)方法测量了一氧化碳分子价壳层分立跃迁的光学振子强度,发现该方法得到的光学振子强度精度较高,可作为实验的基准数据；3、以双原子分子的弹性X射线散射实现了微观尺度下的反冲杨氏双缝实验。一方面,双原子分子可以看做是天然的杨氏双缝,光子的弹性散射强度将呈现出强弱相间的干涉条纹。另一方面,分子的质量较轻,可以测量散射过程中单光子对分子双缝的反冲能量。实验发现同核分子与异核分子有相同的干涉现象,并且所测干涉条纹和反冲能量清晰地表明单个光子是被作为一个整体的双缝散射的,充分验证了“产生干涉时,光子一次通过了两个狭缝”这一超出直观想象的量子力学描述。
[Abstract]:Atomic and molecular physics, has always been an important part of the physical field. Understanding of the molecular structure of a single atom, forming a plasma physics, condensed matter physics, astrophysics, physics and chemistry, material science, biology and other basic research field. The properties of atoms and molecules mainly includes two aspects: the position or momentum space space electronic energy structure and the corresponding experiment. The latter is mainly to explore kinetic parameters based on scattering process, often in the oscillator strength or shape factor (transition matrix element) square that can directly reflect the distribution information of the electronic wave function. Now the measurement of atomic and molecular level structure has reached a very high accuracy (10.16), but the measurement precision of the kinetic parameters are often only a few percent to tens of percent, high precision measurement of common sense there are about 5% The physical mechanism behind the error, and until today the scattering process there are still many uncertainties or disputes. Therefore, developing a new method to obtain kinetic parameters of scattering experiments, experimental benchmark data more accurate, understand the pros and cons of various research methods and research the scattering mechanism, it is very important. At present, the main light experimental study of atomic and molecular oscillator strength or square shape factor absorption method, electron scattering method and X ray scattering method. The optical absorption method can measure the momentum transfer optical oscillator strength is close to zero. The atomic and molecular optical oscillator strength of high energy electron scattering and X ray scattering method can be used to measure the dipole allowed transitions that can also be used to gain momentum and dipole dipole allowed transitions of the transfer kinetics parameter dependent. Method of light absorption and electron scattering. Method for measuring early molecular dynamics parameters, obtained experimental benchmark data in large quantities. High resolution X ray scattering method is different, it is the most recent (2009) was the study group into atomic and molecular field, and as a new method, one can reveal the atomic and molecular collision mechanism on the other hand, can cross check the existed experimental datum, so it has broad application prospects. The main content of this paper is on the basis of the further development of high resolution X ray scattering technique, carry out the optical oscillator strength of atomic and molecular systems research, elastic and non elastic square shape factor. The specific contents are as follows: 1, the non elastic X ray scattering method to obtain the argon atoms, the experimental reference data of hydrogen and nitrogen molecular valence excited square shape factor, which for the first time from the experiment gives the hydrogen and nitrogen molecular electric The shape factor of square sub vibrational excited states. All these measurement results and recent theoretical calculations are in good agreement. The kinetic parameters obtained by comparing the X X-ray scattering experiments and electron scattering experiments, found on electronic system, in high energy electron scattering processes to exist obvious intramolecular scattering, an order the Born approximation is difficult to set up. Also, it is generally believed that the high energy electron scattering experiments at different incident energies of kinetic parameters tend to be consistent, as the first-order Born approximation criterion can be established, but our experimental results clearly show that this criterion is not strictly true, characteristics of higher order Born also showed the incident the electron energy independent; 2, first proposed and implemented to measure optical oscillator strength of dipole (gamma, gamma) method. The optical absorption of photon energy and all carried by self All the momentum is passed to the atoms and molecules, which is characterized by energy transfer (eV), while the larger minimum momentum transfer (10-3a.u.). We propose the use of small angle (2.) to simulate the optical absorption characteristics of momentum transfer minimum X ray scattering process, which can be used to measure the absorption cross section of atoms and molecules of light, we name it is dipole (gamma, gamma) method. This paper uses dipole (gamma, gamma) method for measuring carbon monoxide molecular valence optical oscillator strength of shell discrete transitions, found the optical oscillator strength of high precision obtained by this method, can be used as a benchmark for experimental data; 3, with elastic X ray scattering of diatomic molecules the microscopic recoil of Young's double slit experiment. On the one hand, diatomic molecules can be seen as a natural double slit, elastic scattering intensity of photon interference fringes will appear weak and white. On the other hand, the molecular mass The lighter, can be single photon scattering process of recoil energy molecular double slit. The experimental results showed that with the same interference homonuclear and heteronuclear molecules, and the measured interference fringe and the recoil energy clear single photon is as a whole double slit scattering, fully validated interference when a photon through two slits the beyond the imagination of the description of quantum mechanics.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O561;O434.1

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