RUI: Photon Impact Ionization of Fullerene and Endofullerene Molecules: Cross Sections, Resonances, and Time-Delays

在一个更大的富勒烯笼子里封装一个原子或原子簇，甚至是一个更小的富勒烯(由碳原子组成的巴克球)，提供了一个独特的分子级实验室，在这个实验室中可以在亚纳米到纳米(十亿分之一米)大小的限制下检查客体系统的行为。对这些所谓的内富勒烯的研究不仅可以在原子尺度上产生有趣的效应，还可以探测当前技术可以进入的纳米空间内的过程。事实上，内富勒烯在量子计算、超导、生物医学、药物输送研究、磁共振成像和有机光伏器件等领域有着令人兴奋的应用前景。此外，在地外环境中发现的内富勒烯表明了它们的天体物理学意义。因此，了解限制富勒烯笼子对受限物种行为的影响，反之亦然，是非常有科学意义的事情。对于被限制在富勒烯中的原子，最近的研究预测了原子对辐射的反应会有巨大的增强和变化。然而，如果一团金属原子或较小的富勒烯被限制，这一过程将如何演变尚不清楚。通过研究这种俘虏-俘虏对之间的耦合，研究人员将能够揭示基本效应，从而大大增加当前的知识。有了精确测量的能力，这样的发现将推动涉及团簇掺杂的内富勒烯的实验。此外，产生极短阿秒(十亿分之一秒)激光脉冲的技术进步使人们能够以前所未有的精度研究光-物质相互作用时间。到目前为止，这个程序的结果与Ar原子的时间延迟测量结果是最好的一致。在这一结果的鼓舞下，将启动内富勒烯的阿秒响应研究。这一成果可能会弥合自动科学和纳米科学之间的差距，从而建立一个新的“自动纳米科学”研究领域。最后，另一个计划中的研究领域将专注于在化合物内部的一个位置产生光驱动刺激的过程，随后去刺激到异地转移能量，在新的位置引起戏剧性的反应。目前的计划将访问内富勒烯中的过程，在这些过程中，这种局部刺激可能会引起全球反应。这类似于分子尺度上的天线-接收器对，其中天线耦合到入射光，并在全球范围内传递能量，通过使天线也能够与接收器同步地促进这一过程，从而提高最终输出的效率。这种效应和相关知识可能在纳米天线技术中具有重要的应用价值。这个项目涉及中性和离子内富勒烯对外部光子的响应的理论研究。计算了化合物纯能级和混合能级的光电子截面、角分布、Wigner-Smith时间延迟和库仑间衰变(ICD)共振。这将有助于更好地理解：(I)决定低等离子体能量下吸收、时间和共振衰减性质的多体相互作用；以及(Ii)由于来自化合物不同位置的电子波之间的多路径干扰而产生的衍射型振荡。将研究几个领域。首先，对于被限制在C60中的原子，最近的研究预测了C60等离子体共振能区的原子光致电离的巨大增强。然而，如果金属团簇或较小的富勒烯受到限制，这种耦合将如何演变尚不完全清楚，因为这些系统可以激发自己的等离子体。预计通过研究等离子体激元主动俘获-俘获对之间的耦合，将发现新的效应，从而大大增加目前的知识。凭借最近的精确测量能力，这些发现将推动涉及团簇掺杂或洋葱类型的内富勒烯的实验。其次，对于受限原子，原子内电子的光解放涉及富勒烯壳层的反射。对于原子-富勒烯杂化能级，从原子位置和富勒烯位置都发生了发射。这些发射模式之间的量子多路径干涉携带了大量关于化合物几何结构的信息。用团簇或富勒烯取代内部原子将进一步加剧这种干涉效应，在光致电离截面上产生更丰富的结构，可以用我们最近建立的傅立叶光谱学方法进行诊断，从而显著促进科学知识的发展。库仑间衰变(ICD)过程是原子团中空位的一种自然丰富的非辐射弛豫路径，也是当代研究的热点问题。形成这种空位的前驱体激发可以通过光子或带电粒子碰撞将内壳层电子推进到激发态来完成。内富勒烯是两个同心不等体系的不对称二聚体的旋转类似物，可以诱导新的ICD过程。因此，除了发现基本效应外，这一主题的研究成果还可以产生重大的实验动力。最后，产生阿秒激光脉冲的技术的进步使通过泵浦-探测实验以前所未有的精度研究光-物质相互作用成为可能。内富勒烯的阿秒光电子能谱研究已经启动。这一成果可能会弥合自动科学和纳米科学之间的差距，从而建立一个新的“自动纳米科学”研究领域。

The encapsulation of an atom or a cluster of atoms, or even a smaller fullerene (buckyball made of carbon atoms) inside a larger fullerene cage offers a unique molecular-level laboratory in which to examine the behavior of the guest system in sub-nanometer to nanometer (1 billionth of a meter) size confinements. Studies of these so called endofullerenes can not only lead to intriguing effects at the atomic scale but also can probe processes within the nanometric space that can be accessed by the current technology. In fact, the endofullerenes hold the promise of exciting applications in areas including quantum computations, superconductivity, biomedical fields, drug delivery research, magnetic resonance imaging, and organic photovoltaic devices. Further, the discovery of endofullerenes in extraterrestrial environments indicates their astrophysical relevance. Hence, understanding the influence of the confining fullerene cage on the behavior of the confined species, and vice versa, are matters of great scientific interest. For atoms confined in a fullerene, recent studies have predicted huge enhancements and alterations in the atom's response to radiation. However, it is not known how the process will evolve if instead a cluster of metal atoms or a smaller fullerene is confined. By examining couplings between such captive-captor pairs, researchers will be able to uncover fundamental effects, thereby substantially adding to the current knowledge. With capabilities of precision measurements being available, such findings shall motivate experiments involving cluster-doped endofullerenes. Furthermore, advancements in technology for generating extremely short attosecond (1 billion billionth of a second) laser pulses enable study of the light-matter interaction time with unprecedented precision. Results from this program produced the best agreement so far with the argon atom's time-delay measurements. Encouraged by this result, attosecond response studies of endofullerenes will be initiated. The outcome may bridge the gap between atto- and nano-sciences to establish a new domain of research in 'atto-nano-science'. Finally, another planned research area will focus on processes wherein a light-driven stimulation is caused at one location inside the compound which subsequently de-stimulates to transfer energy off-site to cause a dramatic response in a new location. The current program will access processes in endofullerenes where such local stimulations may cause a global response. This is similar to an antenna-receiver pair at the molecular scale where the antenna couples to the incoming light and transfers energy globally to enhance the efficiency of the ultimate output by enabling the antenna to also contribute to the process in sync with the receiver. The effect and related knowledge may have significant utilization in nanoscale antenna technology. This project involves the theoretical study of the response of neutral and ionic endofullerenes to an external photon. Photoelectron cross sections, angular distributions, Wigner-Smith time delays, and intercoulombic decay (ICD) resonances for both pure and hybrid levels of the compound will be calculated. This will help to understand better: (i) The many-body interactions that determine the absorption, temporal and resonant-decay properties at low plasmonic energies; and (ii) The diffraction-type oscillations due to multipath interferences between electron waves from various sites of the compound. Several areas will be studied. First, for atoms confined in C60, recent studies predicted huge enhancements in the atomic photoionization over the C60 plasmon resonance energy region. However, it is not entirely known how this coupling will evolve if instead a metal cluster or a smaller fullerene is confined, since these systems can excite their own plasmons. It is expected that by examining couplings between the plasmon-active captive-captor pair novel effects will be discovered, thereby substantially adding to the current knowledge. With recent capabilities of precision measurements such findings shall motivate experiments involving cluster-doped or onion-type endofullerenes. Second, for a confined atom the photo-liberation of atomic inner-electrons involves reflection off the fullerene shell. For the atom-fullerene hybrid-levels emissions from both the atomic and the fullerene sites occur. The quantum multipath interference between these modes of emissions carries a wealth of information on the geometry of the compound. Replacing the inner atom by a cluster or a fullerene will further compound this interference effect, producing far richer structures in photoionization cross section that can be diagnosed with our recently established Fourier photospectroscopy methods, thereby, significantly advancing scientific knowledge. Next the intercoulombic decay (ICD) process is a naturally abundant nonradiative relaxation pathway of a vacancy in a cluster and a topic of intense contemporary interest. The precursor excitation to form this vacancy can be accomplished by promoting an inner shell electron to an excited state by the photon or charged particle impact. Endofullerenes, being rotational analogues of asymmetric dimers of two concentric and unequal systems, can induce novel ICD processes. Research results in this topic can, therefore, generate significant experimental impetus, besides discovering fundamental effects. Finally, advancements in technology for generating attosecond laser pulses enable study of the light-matter interaction with unprecedented precision by pump-probe experiments. Attosecond photoemission studies of endofullerenes have been initiated. The outcome may bridge the gap between atto- and nano-sciences to establish a new domain of research in 'atto-nano-science'.