The geometry optimizations and vibrational frequencies of cationic dopamine (DAH+) under different intensity of electric fields (IEFs) are investigated using density function theory (DFT)/B3LYP/6-311G(d,p) and two-dimensional infrared spectra are pictured based on anharmonic approximation. In spite of some differences, the optimized structural parameters calculated by DFT/B3LYP/6-311G(d,p) can well reproduce the experimental ones. Anharmonic approximation greatly improves the agreement between experimental and calculated fundamental frequencies. This study mainly focuses on the potential energy distributions and rotational isomerization of DAH+ under different electric fields. The results showed that there were very strong absorption peaks at 3571 and 3683 cm^–1 for O–H stretching vibrations. The symmetric and asymmetric peaks of C–H stretching vibrations with benzene ring and amidogen were calculated by anharmonic approximation and observed at 2921, 2904, 2997, and 3007 cm^–1. In addition, strong absorption peaks were also observed at 3266, 3313, and 3316 cm^–1 for N–H stretching vibrations. For C–H stretching vibrations with amidogen, when IEF is increasing from −30 × 10^–4 to 20 × 10^–4 a.u., the vibrations of symmetry and asymmetry are coupled. However, the two vibrations were no longer coupled while IEF goes on increasing to 30 × 10^–4 a.u.; For C–H stretching vibrations with benzene ring, the vibrations of symmetry and asymmetry were uncoupled when IEFs are −20 × 10^–4, −10 × 10^–4, 0 × 10^–4, and 30 × 10^–4 a.u. In addition, DAH+ undergoes rotational isomerization only when IEF ranges from −20 × 10^–4 to 10 × 10^–4 a.u.

中文翻译：

---

阳离子多巴胺在不同电场下的二维红外光谱：密度泛函理论非调和势的理论研究

使用密度泛函理论（DFT）/ B3LYP / 6-311G（d，p）研究了不同电场强度（IEF）下阳离子多巴胺（DAH +）的几何优化和振动频率，并基于二维红外光谱图在非谐近似上 尽管存在一些差异，但通过DFT / B3LYP / 6-311G（d，p）计算出的优化结构参数仍可以很好地再现实验参数。非谐波近似极大地改善了实验频率和计算出的基本频率之间的一致性。这项研究主要关注DAH +在不同电场下的势能分布和旋转异构化。结果表明，在3571和3683 cm ^–1处有很强的吸收峰。用于O–H拉伸振动。苯环和酰胺基的CH伸缩振动的对称峰和非对称峰是通过非谐近似计算的，并在2921、2904、2997和3007 cm ^–1处观察到。此外，对于NH拉伸振动，在3266、3313和3316 cm ^–1处也观察到了很强的吸收峰。对于使用^酰胺原的C–H拉伸振动，当IEF从−30×10 ^–4增加到20×10 ^–4 au时，对称振动和非对称振动是耦合的。但是，当IEF继续增加到30×10 ^–4时，这两个振动不再耦合。au; 对于带有苯环的C–H拉伸振动，当IEF为−20×10 ^–4，−10×10 ^–4，0 ×10 ^–4和30×10 ^–4 au时，对称振动和不对称振动是不耦合的。，仅当IEF为−20×10 ^–4到10×10 ^–4 au时，DAH +才经历旋转异构化