RUI: Photoionization, Time Delay, Positronium Formation, and Ion Impact Studies of Fullerenes, Endofullerenes, and Atoms

通过将激光照射在原子上或使原子与带电粒子碰撞，人们可以探测原子对这种外部刺激的反应。这些都是学习材料基本性质的强大科学方法。因此，将这些技术应用于比原子更复杂的系统，并具有直接的应用价值，有利于基础科学和技术的进步。在目前的研究中要研究的系统是巴克富勒烯和其他更大的富勒烯，包括笼在这些分子内的原子/簇，称为内富勒烯。这些材料在量子计算、超导、生物医学领域、药物输送研究、磁共振成像和有机光化学等领域有着令人兴奋的应用前景。因此，了解这些系统的物理和化学结构和响应特性，包括富勒烯笼对受限物种行为的影响，是具有重大科学意义的问题。该计划使用大规模计算机模拟，旨在研究系统内部的电子如何集体相互作用，以内部移动或退出系统，以及它们到达探测器需要多少时间。系统的结构和几何形状如何在机构中起作用？这将被调查的光和快离子的影响。通过选择像正电子这样的外来反粒子来撞击富勒烯，研究电子-正电子对（正电子素）的形成是该计划的一个新方向。这些方法还将用于计算从系统沿着特定方向和/或在所有方向上的出射电子通量的强度。从探测到的电子通量作为激光能量或离子碰撞能量的函数的复杂变化中，研究人员将提取关于系统的有价值的信息。此外，将计算电子从被照射目标到探测器的飞行时间，并且作为激光频率的函数的飞行时间的变化将使人们能够进一步了解科学过程。随着正电子的撞击，正电子素（Ps）的形成是自然界中一个重要的过程，尽管直到最近的研究才尝试使用气相富勒烯系统形成Ps。从Ps形成的研究中学到的科学应该是普遍的Ps形成从纳米系统迎来新的方向Ps光谱学。一般来说，预期结果将激励实验并诱导与实验组的合作。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

By shining the laser light on an atom or by colliding the atom with charged particles one can probe the atom's response to such external stimuli. These are powerful scientific methods to learn fundamental properties of materials. Using these techniques to systems more complex than atoms and of direct applied interest is therefore beneficial for the advancement of basic science and technology. The systems to be studied in the current research are Buckminster fullerenes and other larger fullerenes, including atoms/clusters caged inside these molecules, called endofullerenes. These materials hold the promise of exciting applications in areas including quantum computations, superconductivity, biomedical fields, drug delivery research, magnetic resonance imaging, and organic photovoltaics. Hence, understanding the physical and chemical structure and response properties of these systems, including the influence of the fullerene cage on the behavior of the confined species, are matters of great scientific interest. Using large scale computer simulations the program aims to investigate how electrons inside the systems collectively interacts with each other to move internally or to exit the system and how much time they spend to reach the detector. How do the structure and geometry of the system play roles in the mechanism? This will be investigated both for light and fast-ion impact. By choosing exotic antiparticles like positrons to impact on fullerenes the study of the formation of electron-positron pairs, the positronium, is a novel direction of the program.Numerical methods to be employed to model the systems and their response are based on Density Functional Theory. These methods will also be used to calculate the intensity of the emerging electron flux from the system along a specific direction and/or in all directions. From the complex variation of the detected electron flux as a function of the laser energy or the ion-impact energy researchers will extract valuable information about the system. Furthermore, the time of flight of the electrons from the irradiated target to the detector will be computed and the variation in this flight-time as a function of laser frequency will enable further insights into the scientific processes. Following the impact of positrons, the formation of the positronium (Ps) is a vital process in nature, although no attempt of Ps formation using gas-phase fullerene systems has been made until recent research that came from this program. The science to be learned from the study of Ps formation should be universal for Ps formation from nanosystems ushering new directions of Ps spectroscopy. In general, results are expected to motivate experiments and induce collaborations with experimental groups. Students and postdoctoral researchers will be involved for excellent experience in education and opportunities to become expert researchers.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.