Experimental and theoretical electron momentum spectroscopic study of the valence electronic structure of tetrahydrofuran under pseudorotation.
Experimental and theoretical electron momentum spectroscopic study of the valence electronic structure of tetrahydrofuran under pseudorotation.
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DOI：
10.1021/jp8038658
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发表时间：
2008-10
期刊：
影响因子：
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通讯作者：
C. Ning;Y. Huang;S. F. Zhang;J. Deng;K. Liu;Z. Luo;F. Wang
中科院分区：
文献类型：
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作者：
C. Ning;Y. Huang;S. F. Zhang;J. Deng;K. Liu;Z. Luo;F. Wang
四氢呋喃（THF）中最密集的结构在我们之前的研究中用电子动量谱（EMS）进行了研究。由于前人实验中THF的冲击能相对较低（600 eV），能量分辨率较低（DeltaE = 1.20 eV），所以只研究了THF的最高已占据分子轨道（HOMO）。本研究首次报道了价空间中最新的高分辨率四氢呋喃电子显微镜。分别在1200和2400 eV外加结合能下测量了不同方位角下THF的结合能谱。利用实验得到的结合能谱和轨道动量分布（MDs）研究了THF伪旋转运动的轨道响应。采用外价格林函数（OVGF）、OVGF/6-311++G**模型和基于密度泛函理论（DFT）的SAOP/et-pVQZ模型对结合能谱进行了模拟。轨道动量分布（MDs）采用基于dft的B3LYP/aug-cc-pVTZ模型，结合热力学种群分析。理论与实验结果吻合较好。在1200和2400 eV的冲击能量下，价态轨道的MDs值仅表现出微小的差异，表明平面波脉冲近似（PWIA）的有效性。本研究进一步发现，低动量区HOMO的轨道MDs （p < 0.70 a.u）随赝旋角phi的变化显著，呈v形截面，而THF的最内层价轨道不随赝旋角的变化而变化，揭示了与HOMO完全不同的成键机制。本研究探索了一种研究糖皱缩伪旋的创新方法，为研究其他具有低能垒的生物系统提供了新的思路。
The most populated structure of tetrahydrofuran (THF) has been investigated in our previous study using electron momentum spectroscopy (EMS). Because of the relatively low impact energy (600 eV) and low energy resolution (DeltaE = 1.20 eV) in the previous experiment, only the highest occupied molecular orbital (HOMO) of THF was investigated. The present study reports the most recent high-resolution EMS of THF in the valence space for the first time. The binding energy spectra of THF are measured at 1200 and 2400 eV plus the binding energies, respectively, for a series of azimuthal angles. The experimentally obtained binding energy spectra and orbital momentum distributions (MDs) are employed to study the orbital responses of the pseudorotation motion of THF. The outer valence Greens function (OVGF), the OVGF/6-311++G** model, and density function theory (DFT)-based SAOP/et-pVQZ model are employed to simulate the binding energy spectra. The orbital momentum distributions (MDs) are produced using the DFT-based B3LYP/aug-cc-pVTZ model, incorporating thermodynamic population analysis. Good agreement between theory and experiment is achieved. Orbital MDs of valence orbitals exhibit only slight differences with respect to the impact energies at 1200 and 2400 eV, indicating validation of the plane wave impulse approximation (PWIA). The present study has further discovered that the orbital MDs of the HOMO in the low-momentum region (p < 0.70 a.u) change significantly with the pseudorotation angle, phi, giving a v-shaped cross section, whereas the innermost valence orbital of THF does not vary with pseudorotation, revealing a very different bonding mechanism from the HOMO. The present study explores an innovative approach to study pseudorotation of sugar puckering, which sheds a light to study other biological systems with low energy barriers among ring-puckering conformations.