Vibrational exciton coupling in homo and hetero dimers of carboxylic acids studied by linear infrared and Raman jet spectroscopy.
Vibrational exciton coupling in homo and hetero dimers of carboxylic acids studied by linear infrared and Raman jet spectroscopy.
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DOI：
10.1063/1.5043400
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发表时间：
2018-09
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通讯作者：
K. Meyer;M. Suhm
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作者：
K. Meyer;M. Suhm
由甲酸，乙酸和特戊酸组成的三个杂二聚体的C=O伸缩振动的喷射冷却带的位置已被确定。在对称拉伸模式的共振模式已被校正，通过假设一个单一的明亮的状态。对它们的Davydov或振动激子分裂的分析表明，杂二聚体值可以从各自的均二聚体分裂（范围从乙酸的56 cm-1到甲酸二聚体的75 cm-1）平均，误差≤ 7%。由双氢键引起的6个激子分裂和6个独立的下移的集合作为计算方法的基准测试的参考数据库。B3 LYP被证明是无法描述的甲酸和乙酸单体之间的差异，但在其他方面是令人满意的，如果假设激子分裂只有微弱的非谐效应超出去卷积局部共振的影响。然而，振动微扰理论测试点在显着的对角非谐效应的激子分裂。自旋分量标度和规范MP2未能再现实验二聚体位移和分裂的谐波近似，但预计非谐波校正，以提高性能。Harmonic PBEH-3c在缩放后很好地再现了实验数据集。实验数据设置的阶段，更严格的多维耦合的羧酸二聚体和三聚体中的C=O振荡器的非谐波治疗。此外，我们报告的第一个振动喷流光谱的顺式甲酸在C=O伸缩区加热喷嘴和喷嘴馈线的拉曼装置。
The jet-cooled band positions of the C=O stretching vibrations in the three hetero dimers composed of formic, acetic, and pivalic acid have been determined. Resonance patterns in the symmetric stretching modes have been corrected for by assuming a single bright state. An analysis of their Davydov or vibrational exciton splitting shows that the hetero dimer values can be averaged from the respective homo dimer splittings (ranging from 56 cm-1 for the acetic to 75 cm-1 for the formic acid dimer) with an error of ≤7%. The set of 6 exciton splittings and 6 independent downshifts caused by double hydrogen bonding serves as a reference data base for the benchmarking of computational methods. B3LYP is shown to be unable to describe the difference between the formic and acetic acid monomer but is otherwise satisfactory, if one assumes that exciton splittings are only weakly affected by anharmonic effects beyond the deconvoluted local resonances. However, a vibrational perturbation theory test points at significant diagonal anharmonicity effects for the exciton splitting. Spin-component-scaled and canonical MP2 fail in reproducing experimental dimer shifts and splittings in the harmonic approximation, but anharmonic corrections are expected to improve the performance. Harmonic PBEh-3c reproduces the experimental data set well after scaling. The experimental data set the stage for more rigorous anharmonic treatments of the multidimensional coupling of C=O oscillators in carboxylic acid dimers and trimers. In addition, we report the first vibrational jet spectrum of cis-formic acid in the C=O stretching region by heating the nozzle and the nozzle feed line of the Raman setup.