Lehr Andreas, Rivic Filip, Jäger Marc, Gleditzsch Martin, Schäfer Rolf
Technical University of Darmstadt, Eduard-Zintl-Institut, Alarich-Weiss-Straße 8, 64287 Darmstadt, Germany.
Phys Chem Chem Phys. 2022 May 18;24(19):11616-11635. doi: 10.1039/d2cp01171a.
Neutral Sn clusters with = 6-20, 25, 30, 40 are investigated in a joint experimental and quantum chemical study with the aim to reveal their optical absorption in conjunction with their structural evolution. Electric beam deflection and photodissociation spectroscopy are applied as molecular beam techniques at nozzle temperatures of 16 K, 32 K and 300 K. The dielectric response is probed following the approach in S. Schäfer , 2008, , 12312-12319. It is improved on those findings and the cluster size range is extended in order to cover the prolate growth regime. The impact of the electric dipole moment, rotational temperature and vibrational excitation on the deflection profiles is discussed thoroughly. Photodissociation spectra of tin clusters are recorded for the first time, show similarities to spectra of silicon clusters and are demonstrated to be significantly complicated by the presence of multiphoton absorption in the low-energy region and large excess energies upon dissociation which is modelled by the RRKM theory. In both experiments two isomers for the clusters with = 8, 11, 12, 19 need to be considered to explain the experimental results. Triple-capped trigonal prisms and double-capped square antiprisms are confirmed to be the driving building units for almost the entire size range. Three dominating fragmentation channels are observed, the loss of a tin atom for < 12, a Sn fragment for < 19 and a Sn fragment for ≥ 19 with Sn subunits constituting recurring geometric motifs for > 20. The prolate-to-quasispherical structural transition is found to occur at 30 < ≤ 40 and is analyzed with respect to the observed optical behavior taking quantum chemical calculations and the Mie-Gans theory into account. Limitations of the experimental approach to study the geometric and electronic structure of the clusters at elevated temperatures due to vibrational excitation is also thoroughly discussed.
在一项联合实验与量子化学研究中，对具有(n = 6 - 20)、(25)、(30)、(40)的中性锡团簇进行了研究，目的是揭示它们的光吸收及其结构演变。在(16K)、(32K)和(300K)的喷嘴温度下，采用电子束偏转和光解离光谱作为分子束技术。按照S. Schäfer 2008年文献（文献编号，12312 - 12319）中的方法探测介电响应。在此基础上进行了改进，并扩展了团簇尺寸范围，以涵盖长轴生长模式。深入讨论了电偶极矩、转动温度和振动激发对偏转轮廓的影响。首次记录了锡团簇的光解离光谱，其与硅团簇光谱相似，并且证明由于低能区多光子吸收的存在以及解离时的大量过剩能量（由RRKM理论建模），使得光谱显著复杂化。在两个实验中，对于(n = 8)、(11)、(12)、(19)的团簇，需要考虑两种异构体来解释实验结果。确认三棱柱三重帽和双帽四方反棱柱几乎是整个尺寸范围内的驱动构建单元。观察到三个主要的碎片化通道，对于(n < 12)，损失一个锡原子；对于(n < 19)，损失一个(Sn)片段；对于(n≥19)，损失一个(Sn)片段，对于(n > 20)，(Sn)亚基构成重复的几何图案。发现长轴到准球形的结构转变发生在(30 < n ≤ 40)，并结合量子化学计算和米氏 - 甘斯理论，针对观察到的光学行为进行了分析。还深入讨论了由于振动激发，在高温下研究团簇几何和电子结构的实验方法的局限性。
