Ning C G, Huang Y R, Zhang S F, Deng J K, Liu K, Luo Z H, Wang F
Department of Physics and Key Laboratory of Atomic and Molecular NanoSciences of MOE, Tsinghua University, Beijing 100084, People's Republic of China.
J Phys Chem A. 2008 Nov 6;112(44):11078-87. doi: 10.1021/jp8038658. Epub 2008 Oct 9.
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.
在我们之前的研究中，利用电子动量谱（EMS）对四氢呋喃（THF）的最密集结构进行了研究。由于之前实验中的碰撞能量相对较低（600 eV）且能量分辨率较低（ΔE = 1.20 eV），因此仅对THF的最高占据分子轨道（HOMO）进行了研究。本研究首次报道了THF在价空间中的最新高分辨率EMS。分别在1200 eV和2400 eV加上结合能的条件下，针对一系列方位角测量了THF的结合能谱。利用实验获得的结合能谱和轨道动量分布（MDs）来研究THF假旋转运动的轨道响应。采用外层价格林函数（OVGF）、OVGF/6 - 311++G**模型以及基于密度泛函理论（DFT）的SAOP/et - pVQZ模型来模拟结合能谱。使用基于DFT的B3LYP/aug - cc - pVTZ模型并结合热力学布居分析来生成轨道动量分布（MDs）。理论与实验之间取得了良好的一致性。价轨道的轨道MDs在1200 eV和2400 eV的碰撞能量下仅表现出微小差异，这表明平面波脉冲近似（PWIA）是有效的。本研究进一步发现，低动量区域（p < 0.70 a.u）中HOMO的轨道MDs随假旋转角φ发生显著变化，呈现出V形截面，而THF的最内层价轨道不随假旋转变化，这揭示了与HOMO非常不同的成键机制。本研究探索了一种研究糖环皱缩假旋转的创新方法，为研究其他在环皱缩构象间具有低能垒的生物系统提供了思路。
