Department of Physics, State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084, People's Republic of China.
J Chem Phys. 2012 Mar 28;136(12):124302. doi: 10.1063/1.3696028.
The ionization energy spectra and electron momentum distributions of formamide were investigated using the high-resolution electron momentum spectrometer in combination with high level calculations. The observed ionization energy spectra and electron momentum distributions were interpreted using symmetry adapted cluster-configuration interaction theory, outer valence Green function, and DFT-B3LYP methods. The ordering of 10a(') and 2a(") orbitals of formamide was assigned unambiguously by comparing the experimental electron momentum distributions with the corresponding theoretical results, i.e., 10a(') has a lower binding energy. In addition, it was found that the low-frequency wagging vibration of the amino group at room temperature has noticeable effects on the electron momentum distributions. The equilibrium-nuclear-positions-approximation, which was widely used in electron momentum spectroscopy, is not accurate for formamide molecule. The calculations based on the thermal average can evidently improve the agreement with the experimental momentum distributions.
采用高分辨率电子动量谱仪结合高精度计算，研究了甲酰胺的电离能谱和电子动量分布。利用对称自适应簇构型相互作用理论、外价格林函数和 DFT-B3LYP 方法对观测到的电离能谱和电子动量分布进行了解释。通过将实验电子动量分布与相应的理论结果进行比较，明确地确定了甲酰胺中 10a(') 和 2a(") 轨道的排列顺序，即 10a(') 具有较低的结合能。此外，还发现室温下氨基的低频摇摆振动对电子动量分布有明显影响。在电子动量谱学中广泛使用的平衡核位置近似对于甲酰胺分子并不准确。基于热平均的计算可以明显提高与实验动量分布的一致性。
