Zubarev Dmitry Yu, Alexandrova Anastassia N, Boldyrev Alexander I, Cui Li-Feng, Li Xi, Wang Lai-Sheng
Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300, USA.
J Chem Phys. 2006 Mar 28;124(12):124305. doi: 10.1063/1.2177254.
Photoelectron spectroscopy was combined with ab initio calculations to elucidate the structure and bonding in Si6 2- and NaSi6 -. Well-resolved electronic transitions were observed in the photoelectron spectra of Si6 - and NaSi6 - at three photon energies (355, 266, and 193 nm). The spectra of NaSi6 - were observed to be similar to those of Si6 - except that the electron binding energies of the former are lower, suggesting that the Si6 motif in NaSi6 - is structurally and electronically similar to that in Si6 -. The electron affinities of Si6 and NaSi6 were measured fairly accurately to be 2.23+/-0.03 eV and 1.80+/-0.05 eV, respectively. Global minimum structure searches for Si6 2- and NaSi6 - were performed using gradient embedded genetic algorithm followed by B3LYP, MP2, and CCSDT calculations. Vertical electron detachment energies were calculated for the lowest Si6 - and NaSi6 - structures at the CCSD(T)/6-311+G(2df), ROVGF/6-311+G(2df), UOVGF/6-311+G(2d), and time-dependent B3LYP/6-311+G(2df) levels of theory. Experimental vertical detachment energies were used to verify the global minimum structure for NaSi6 -. Though the octahedral Si6 2-, analogous to the closo form of borane B6H6 2-, is the most stable form for the bare hexasilicon dianion, it is not the kernel for the NaSi6 - global minimum. The most stable isomer of NaSi6 - is based on a Si6 2- motif, which is distorted into C2v symmetry similar to the ground state structure of Si6 -. The octahedral Si6 2- coordinated by a Na+ is a low-lying isomer and was also observed experimentally. The chemical bonding in Si6 2- and NaSi6 - was understood using natural bond orbital, molecular orbital, and electron localization function analyses.
光电子能谱与从头算计算相结合，以阐明Si6 2-和NaSi6 -的结构和键合。在Si6 -和NaSi6 -的光电子能谱中，在三种光子能量（355、266和193 nm）下观察到了分辨良好的电子跃迁。观察到NaSi6 -的光谱与Si6 -的光谱相似，只是前者的电子结合能较低，这表明NaSi6 -中的Si6结构单元在结构和电子性质上与Si6 -中的相似。Si6和NaSi6的电子亲和能被相当准确地测量为分别为2.23±0.03 eV和1.80±0.05 eV。使用梯度嵌入遗传算法，随后进行B3LYP、MP2和CCSDT计算，对Si6 2-和NaSi6 -进行了全局最小结构搜索。在CCSD(T)/6-311+G(2df)、ROVGF/6-311+G(2df)、UOVGF/6-311+G(2d)和含时B3LYP/6-311+G(2df)理论水平下，计算了最低Si6 -和NaSi6 -结构的垂直电子脱离能。实验垂直脱离能用于验证NaSi6 -的全局最小结构。尽管类似于硼烷B6H6 2-的封闭形式的八面体Si6 2-是裸六硅双阴离子最稳定的形式，但它不是NaSi6 -全局最小值的核心。NaSi6 -最稳定的异构体基于Si6 2-结构单元，其扭曲成与Si6 -基态结构相似的C2v对称性。由Na+配位的八面体Si6 2-是一个低能异构体，也通过实验观察到。使用自然键轨道、分子轨道和电子定域函数分析来理解Si6 2-和NaSi6 -中的化学键。
