Institut für Physikalische Chemie, Universität Göttingen, Tammannstr. 6, 37077 Göttingen, Germany.
Deutsches Elektronen-Synchrotron, Notkestr. 85, 22607 Hamburg, Germany.
J Chem Phys. 2020 Apr 30;152(16):164303. doi: 10.1063/5.0004465.
The site-specific first microsolvation step of furan and some of its derivatives with methanol is explored to benchmark the ability of quantum-chemical methods to describe the structure, energetics, and vibrational spectrum at low temperature. Infrared and microwave spectra in supersonic jet expansions are used to quantify the docking preference and some relevant quantum states of the model complexes. Microwave spectroscopy strictly rules out in-plane docking of methanol as opposed to the top coordination of the aromatic ring. Contrasting comparison strategies, which emphasize either the experimental or the theoretical input, are explored. Within the harmonic approximation, only a few composite computational approaches are able to achieve a satisfactory performance. Deuteration experiments suggest that the harmonic treatment itself is largely justified for the zero-point energy, likely and by design due to the systematic cancellation of important anharmonic contributions between the docking variants. Therefore, discrepancies between experiment and theory for the isomer abundance are tentatively assigned to electronic structure deficiencies, but uncertainties remain on the nuclear dynamics side. Attempts to include anharmonic contributions indicate that for systems of this size, a uniform treatment of anharmonicity with systematically improved performance is not yet in sight.
我们探索了呋喃及其一些衍生物与甲醇的特定位置的首次微溶剂化步骤，以基准量子化学方法在低温下描述结构、能量和振动光谱的能力。在超音速射流膨胀中使用红外和微波光谱来量化模型配合物的对接偏好和一些相关的量子态。微波光谱严格排除甲醇的面内对接，而支持芳环的顶部配位。我们探索了强调实验或理论输入的对比对比策略。在谐波近似中，只有少数复合计算方法能够达到令人满意的性能。氘化实验表明，由于对接变体之间重要的非谐贡献的系统抵消，谐波处理本身在零点能方面是合理的，这可能是有意为之。因此，实验和理论之间的异构体丰度差异被暂时归因于电子结构缺陷，但核动力学方面仍存在不确定性。尝试包括非谐贡献表明，对于这种大小的系统，具有系统改进性能的非谐性统一处理还没有出现。
