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Ultrafast Strong-Field Vibrational Dynamics Studied by Femtosecond Extreme-Ultraviolet Transient Absorption Spectroscopy.

机译：飞秒极紫外瞬态吸收光谱研究超快强场振动动力学。

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摘要

Femtosecond time-resolved extreme-ultraviolet core-level absorption spectroscopy has developed into a powerful tool for investigating chemical dynamics due to its sensitivity for detecting changes in electronic structure. By probing the core-levels of atoms and molecules, dynamics may be monitored with elemental specificity, as well as localized sensitivity to the oxidation state around the atomic absorber. In this thesis, the complete reconditioning of the experimental apparatus is described and its application to the study of vibrational wave packets created by strong-field ionization of Br2 is discussed.;First, extreme-ultraviolet transient absorption is established as a bond-length specific probe capable of resolving vibrational motion in Br2 and Br2+ due to a change in the transition amplitude and energy versus bond length of the 3d5/2,3/2 core-level transitions to unoccupied molecular orbitals. Furthermore, the degree of coherence and beat composition of the S+g1 ground state vibrational wave packet is established. Second, the preparation of vibrational wave packets by strong-field ionization of Br2 is analyzed as a function of field intensity. At a field intensity near the threshold of ionization, selective depletion of the vibrational amplitude is observed near the inner turning point, corresponding to the minimum in the ionization energy for the unperturbed molecular potential energy curves. The observed superposition is determined to be primarily composed of the nu0nu 1 vibrational beat. As the field intensity is increased, perturbation of the potential curves results in preparation of the wave packet at longer internuclear separations, and the distortion of the potentials is directly observed by a shift in the core-level transition energy within the intense laser pulse. Moreover, the composition of the wave packet is found to involve higher vibrational levels, indicating the involvement of a Raman pumping mechanism in the preparation of the superposition. Third, several ongoing experiments utilize the unique instrumental capabilities including the elemental specificity and polarization dependence of the absorption. The elemental specificity and nuclear motion dependence of the core-level probe is utilized to investigate the correlated detection of vibrational wave packet dynamics in IBr on the iodine 4d and bromine 3d core-level absorptions simultaneously. Also, polarization dependent absorption of Xe2+ looks to extend the quantitative measurements conducted for Xe+ to determine the complete |j, m⟩ state populations after sequential ionization. Lastly, polarization dependent measurements of the strong-field ionization of Br2 suggest alignment between the molecular axis and the electric field of the ionizing pump at field intensities near the threshold for ionization, which is lost at higher field strengths. These studies expand the repertoire of capabilities for high-order harmonic generation beyond the proof of principle experiments and establish the technique as a practical tool for monitoring complex, ultrafast molecular dynamics by core-level probing.;A theoretical model for determining the sensitivity of XUV absorption to valence vibrational motion generated by strong-field ionization was developed. This theoretical model, including details of traditional Ammosov-Delone-Krainov tunnel ionization rates, is presented in Chapter 2. Chapter 3 describes the experimental changes incorporated into the apparatus for successful multi-day experiments for the determination of vibrational dynamics with ~1 cm -1 spectral resolution. Demonstration of the sensitivity of XUV transient absorption to non-stationary ground state vibrational dynamics is then presented in Chapter 4, investigating the vibrational superposition generated in Br 2 after irradiation with a 1.6 x 1014 W/cm 2 driving pump pulse. Chapter 5 expounds upon the dependence on field intensity to the observed vibrational dynamics in Br2 as well as Br2+. Chapter 6 discusses the currently ongoing experiments being conducted for ground state vibrational wave packet preparation in iodine monobromide, the determination of the complete |j, m⟩ quantum state population of Xe2+, and the alignment of the molecular axis of Br2 with the electric field of the ionizing 800 nm field following strong-field ionization. Chapter 6 also presents the conclusions of the experimental work presented here as well as the future outlook of XUV transient absorption spectroscopy in the broader perspective of investigating chemical reaction and dynamics. (Abstract shortened by UMI.).
机译：飞秒时间分辨的极端紫外核能级吸收光谱法已经发展成为研究化学动力学的强大工具，因为它对检测电子结构的变化具有敏感性。通过探测原子和分子的核心水平，可以用元素特异性以及对原子吸收剂周围氧化态的局部敏感性来监测动力学。本文描述了实验装置的完全修复，并讨论了其在研究Br2强场电离产生的振动波包中的应用。首先，建立了极紫外瞬态吸收作为键长特异性的方法。探针能够解决Br2和Br2 +中的振动运动，这是由于跃迁幅度和能量随3d5 / 2,3 / 2核级跃迁到未占据分子轨道的键长的变化而变化的。此外，确定了S + g1基态振动波包的相干度和拍频成分。其次，分析了通过Br2的强场电离制备振动波包，并作为场强的函数。在接近电离阈值的场强下，在内部转折点附近观察到振动幅度的选择性消耗，这对应于未受干扰的分子势能曲线的电离能的最小值。确定观察到的叠加主要由nu0nu 1振动拍组成。随着场强的增加，电势曲线的扰动会导致在较长的核间间隔处形成波包，并且通过强烈激光脉冲中核心能级跃迁能的移动直接观察到电势的畸变。此外，发现波包的组成涉及较高的振动水平，这表明拉曼泵浦机构参与了叠加的准备。第三，一些正在进行的实验利用了独特的仪器功能，包括吸收的元素特异性和极化依赖性。利用核心水平探针的元素特异性和核运动依赖性，研究了同时对碘4d和溴3d核心水平吸收进行的IBr振动波包动力学的相关检测。同样，Xe2 +的极化依赖性吸收看起来可以扩展对Xe +进行的定量测量，从而确定在顺序电离后确定完整的| j，m〉状态种群。最后，Br2的强场电离的极化相关测量表明，在接近电离阈值的场强下，分子轴与电离泵电场之间的对齐方式在电离阈值附近会丢失。这些研究扩大了高次谐波产生能力的范围，超出了原理实验的证明，并将该技术确立为通过核心水平探测监测复杂，超快分子动力学的实用工具。;确定XUV灵敏度的理论模型开发了由强场电离产生的化合价振动运动。第2章介绍了该理论模型，其中包括传统的Ammosov-Delone-Krainov隧道电离速率的详细信息。第3章介绍了设备中的实验变化，用于成功地进行多天实验，确定了约1 cm-的振动动力学。 1个光谱分辨率。然后，在第4章中介绍了XUV瞬态吸收对非平稳基态振动动力学的敏感性，研究了用1.6 x 1014 W / cm 2驱动泵浦脉冲辐照后Br 2中产生的振动叠加。第5章阐述了磁场强度对Br2以及Br2 +中所观察到的振动动力学的依赖性。第6章讨论了正在进行的一溴化碘基态振动波包制备实验，Xe2 +的完整| j，m〉量子态种群的确定以及Br2分子轴与电场的对准。在强场电离后电离800 nm场。第6章还从更广泛的角度研究化学反应和动力学的角度，介绍了此处提出的实验工作的结论以及XUV瞬态吸收光谱的未来前景。 （摘要由UMI缩短。）。

著录项

  • 作者

    Hosler, Erik Robert.;

  • 作者单位

    University of California, Berkeley.;

  • 授予单位 University of California, Berkeley.;
  • 学科 Chemistry Physical.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 220 p.
  • 总页数 220
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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