Felker Peter M, Vlček Vojtěch, Hietanen Isaac, FitzGerald Stephen, Neuhauser Daniel, Bačić Zlatko
Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-1569, USA.
Phys Chem Chem Phys. 2017 Nov 29;19(46):31274-31283. doi: 10.1039/c7cp06062a.
Symmetry breaking has been recently observed in the endofullerenes M@C (M = H, HF, HO), manifesting in the splittings of the three-fold degenerate ground states of the endohedral ortho-H, ortho-HO and the j = 1 level of HF. The nature of the interaction causing the symmetry breaking is established in this study. A fragment of the solid C is considered, comprised of the central C molecule surrounded by twelve nearest-neighbor (NN) C molecules. The fullerenes have either P (major) or H (minor) orientational orderings, and are assumed to be rigid with I symmetry. Only the central C is occupied by the guest molecule M, while the NN fullerenes are all empty. The key proposition of the study is that the electrostatic interactions between the charge densities on the NN C molecules and that on M inside the central C give rise to the symmetry breaking responsible for the measured level splittings. Using this model, the M@C level splittings of interest are calculated variationally and using perturbation theory, for both the P and H orientations. Those obtained for the dominant P orientation are in excellent agreement with the experimental results, with respect to the splitting magnitudes and patterns, for all three M@C systems considered, pointing strongly to the quadrupolar M-NN interactions as the main cause of the symmetry breaking. The level splittings calculated for the H orientation are about 30 times smaller than the ones in the P orientation.
最近在内富勒烯M@C（M = H、HF、HO）中观察到了对称性破缺，表现为内笼中邻位H、邻位HO的三重简并基态以及HF的j = 1能级的分裂。本研究确定了导致对称性破缺的相互作用的本质。考虑固态C的一个片段，它由中心C分子及其周围的十二个最近邻（NN）C分子组成。富勒烯具有P（主要）或H（次要）取向有序性，并假定具有I对称性的刚性结构。仅中心C被客体分子M占据，而NN富勒烯均为空的。该研究的关键命题是，NN C分子上的电荷密度与中心C内部M上的电荷密度之间的静电相互作用导致了对称性破缺，从而造成了所测量的能级分裂。使用该模型，对P和H取向的感兴趣的M@C能级分裂进行了变分计算和微扰理论计算。对于占主导的P取向所获得的结果，在所考虑的所有三个M@C系统的分裂幅度和模式方面，与实验结果非常吻合，强烈表明四极M-NN相互作用是对称性破缺的主要原因（。对于H取向计算的能级分裂比P取向的小约30倍。 ） 括号中为调整了语序使语句更通顺的内容，原文最后一句逻辑较松散，翻译时适当调整了语序使表达更清晰。
