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

将一个原子或一簇原子，甚至是一个较小的富勒烯（由碳原子制成的巴基球）封装在一个较大的富勒烯笼中，提供了一个独特的分子水平实验室，可以在亚纳米到纳米（十亿分之一米）尺寸的限制中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，而且还可以探测当前技术可以访问的纳米空间内的过程。 事实上，内富勒烯在量子计算、超导、生物医学领域、药物递送研究、磁共振成像和有机光伏器件等领域都有令人兴奋的应用前景。此外，在地外环境中发现内富勒烯表明了它们与天体物理学的相关性。 因此，理解封闭的富勒烯笼对封闭物种行为的影响，反之亦然，是具有重大科学意义的问题。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的巨大增强和改变。然而，目前还不知道如果金属原子簇或更小的富勒烯被限制，该过程将如何演变。通过研究这种捕获-捕获对之间的耦合，研究人员将能够揭示基本效应，从而大大增加了现有的知识。随着精确测量的能力，这样的发现将激励涉及簇掺杂的内富勒烯的实验。此外，产生极短阿秒（十亿亿分之一秒）激光脉冲的技术进步使得能够以前所未有的精度研究光与物质的相互作用时间。这个程序的结果与氩原子的时间延迟测量结果迄今为止最吻合。受这一结果的鼓舞，将启动对内富勒烯的阿秒响应研究。这一成果可能会弥合阿托科学与纳米科学之间的差距，建立一个新的研究领域“阿托纳米科学”。最后，另一个计划的研究领域将集中在过程中，其中光驱动的刺激是在化合物内的一个位置引起的，随后去刺激转移能量到场外，在一个新的位置引起显着的反应。目前的计划将访问过程中的内富勒烯，这种局部刺激可能会导致一个全球性的反应。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全局地传输能量，以通过使天线也能够与接收器同步地对该过程做出贡献来提高最终输出的效率。该效应及其相关知识在纳米天线技术中具有重要的应用价值。 该项目涉及中性和离子型富勒烯对外部光子的响应的理论研究。光电子截面，角分布，Wigner-Smith时间延迟，和intercoulombic衰减（ICD）共振的纯和混合水平的化合物将被计算。这将有助于更好地理解：（i）在低等离子体能量下确定吸收，时间和共振衰减特性的多体相互作用;以及（ii）由于来自化合物各个位置的电子波之间的多径干扰而引起的衍射型振荡。将研究几个领域。首先，对于被限制在C60中的原子，最近的研究预测了在C60等离子体共振能量区域上原子光电离的巨大增强。然而，如果金属簇或较小的富勒烯被限制，这种耦合将如何演变还不完全清楚，因为这些系统可以激发它们自己的等离子体激元。预期通过检查等离子体活性俘获-俘获子对之间的耦合，将发现新的效应，从而大大增加了现有的知识。随着最近的精确测量能力，这些发现将激励涉及簇掺杂或洋葱型内富勒烯的实验。第二，对于受限原子，原子内电子的光释放涉及富勒烯壳层的反射。对于原子-富勒烯混合能级，原子和富勒烯位点都发生发射。这些发射模式之间的量子多径干涉携带了关于化合物几何形状的丰富信息。用团簇或富勒烯取代内部原子将进一步复合这种干涉效应，在光电离截面中产生更丰富的结构，可以用我们最近建立的傅立叶光谱方法进行诊断，从而显着推进科学知识。其次，间库仑衰变（ICD）过程是一个自然丰富的非辐射弛豫路径的空缺在一个集群和一个激烈的当代感兴趣的话题。形成这种空位的前体激发可以通过由光子或带电粒子碰撞将内壳层电子促进到激发态来实现。内富勒烯，作为两个同心和不等系统的不对称二聚体的旋转类似物，可以诱导新的ICD过程。因此，这一主题的研究结果除了发现基本效应外，还可以产生重要的实验推动力。最后，产生阿秒激光脉冲的技术进步使得通过泵浦-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开始。这一成果可能会弥合阿托科学与纳米科学之间的差距，建立一个新的研究领域“阿托纳米科学”。

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'.