Dipartimento di Chimica, Università degli Studi di Milano, via C. Golgi 19, 20133, Milano, Italy.
Istituto Nazionale di Ricerca Metrologica, Strada delle Cacce 91, 10135, Torino, Italy.
Nat Commun. 2020 Aug 28;11(1):4348. doi: 10.1038/s41467-020-18211-3.
The interpretation of molecular vibrational spectroscopic signals in terms of atomic motion is essential to understand molecular mechanisms and for chemical characterization. The signals are usually assigned after harmonic normal mode analysis, even if molecular vibrations are known to be anharmonic. Here we obtain the quantum anharmonic vibrational eigenfunctions of the 11-atom protonated glycine molecule and we calculate the density distribution of its nuclei and its geometry parameters, for both the ground and the O-H stretch excited states, using our semiclassical method based on ab initio molecular dynamics trajectories. Our quantum mechanical results describe a molecule elongated and more flexible with respect to what previously thought. More importantly, our method is able to assign each spectral peak in vibrational spectroscopy by showing quantitatively how normal modes involving different functional groups cooperate to originate that spectroscopic signal. The method will possibly allow for a better rationalization of experimental spectroscopy.
从原子运动的角度来解释分子振动光谱信号对于理解分子机制和化学特性至关重要。这些信号通常是在进行谐波正则模式分析后进行分配的，即使分子振动是已知的非谐性的。在这里，我们获得了 11 个原子的质子化甘氨酸分子的量子非谐振动本征函数，并使用基于从头算分子动力学轨迹的半经典方法计算了其原子核的密度分布及其几何参数，分别对应于基态和 O-H 伸缩激发态。我们的量子力学结果表明，与之前的假设相比，分子被拉长且更具柔韧性。更重要的是，我们的方法能够通过定量地展示涉及不同官能团的正则模式如何协作产生该光谱信号来为振动光谱中的每个光谱峰进行分配。该方法可能会使实验光谱学的合理化得到更好的解释。
