Attosecond Resolved Photoionization Studies of Atomic and Molecular Dynamics

在这个项目中，物理学家将尝试测量一个原子或分子中发生了什么，当一个紧密结合的电子被x射线脉冲移除后，原子或分子处于激发状态，最终衰减到较低的能量构型。这项工作将集中在一种特定的衰变模式(俄歇衰变)上，在这种模式下，被激发的原子或分子会喷射出另一个(松散束缚的)电子来带走多余的能量。在这里，俄歇衰变预计需要大约100阿秒(0.0000000000000001秒)。俄歇衰变后，分子很可能会分裂成碎片，只留下组成它的原子。实验人员将尝试测量俄歇衰变时间，并将其与释放的碎片类型以及其他测量量相关联。这项研究将有助于阐明我们对分子分裂过程中的量子力学过程的理解，特别是我们对俄歇衰变过程的基本理解。此外，预计这将作为至少一名博士生论文、几名本科生高级论文以及一名博士后研究员就业和培训的基础。这项拟议的实验将尝试测量氙气中碘甲烷(CH3I)中俄歇衰变的时间分辨动力学，并扩展我们对二氯乙烯(C2H2Cl2)的初步研究。本实验将使用成熟的冷靶反冲离子动量谱(COLTRIMS)技术来同时确定气相分子框架(即实验室框架中的分子取向)和俄歇衰变时间。对定时信息的访问是通过测量电子动量和了解电场的时间相关性质来实现的。在本实验中，含时电场由原子或分子系统通过俄歇衰变提供。这项实验将扩大我们对原子和分子系统在超快俄歇衰变后所涉及的动力学的理解。在分子系统的情况下，实验人员将尝试确定俄歇衰变时间和分子框角分布(MFPAD)之间的相关性。MFPAD对分子势能高度敏感，至少在原则上可以用来收集有关分子势能的信息(即光电子被抛出时分子组成原子在太空中的构型)。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

In this project, physicists will attempt to measure what happens in an atom or molecule after a tightly bound electron is removed by a pulse of x-ray light, leaving the atom or molecule in an excited state which eventually decays to a lower energy configuration. The work will focus on a specific mode of decay (Auger decay) in which the excited atom or molecule ejects another (loosely bound) electron to carry away the excess energy. Here the Auger decay is expected to take around 100 attoseconds (0.0000000000000001 seconds). After Auger decay, a molecule will likely break up into pieces, leaving only its constituent atoms. The experimenters will try to measure this Auger decay time and correlate it with the type of fragments that are released, along with other measured quantities. This study will help illuminate our understanding of the quantum mechanical processes that play out during molecular breakup, and in particular our fundamental understanding of the Auger decay process. Additionally, it is expected that this will serve as the basis for at least one Ph.D. student’s dissertation, several undergraduate students' senior theses, and the employment and training of a postdoctoral fellow. This proposed experiment will attempt to measure the time-resolved dynamics of Auger decay in xenon, methyl iodide (CH3I), and expand our preliminary studies of dichloroethylene (C2H2Cl2). This experiment will employ the well-established COLd Target Recoil Ion Momentum Spectroscopy (COLTRIMS) technique to simultaneously determine the gas-phase molecular frame (i.e. molecular orientation in the laboratory frame), and the Auger decay time. Access to the timing information is achieved through the measurement of the electron momentum and knowledge of the time-dependent nature of the electric field. In this experiment the time-dependent electric field is supplied by the atomic or molecular system via the Auger decay. This experiment will expand our understanding of the dynamics involved in atomic and molecular systems following the ultrafast Auger decay. In the case of molecular systems, the experimenters will attempt to determine the correlation between the Auger decay timing and the Molecular Frame Angular Distribution (MFPAD). The MFPAD is highly sensitive to the molecular potential and at least in principle could be used to glean information about the molecular potential (i.e. the configuration of the molecule’s constituent atoms in space at the “moment” the photoelectron is ejected).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.