Guńka Piotr A, Zhu Li, Strobel Timothy A, Zachara Janusz
Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warszawa, Poland.
Earth and Planets Laboratory, Carnegie Institution for Science, 5251 Broad Branch Road NW, Washington, DC 20015, USA.
J Chem Phys. 2020 Aug 7;153(5):054501. doi: 10.1063/5.0017892.
Raman spectroscopic measurements of the arsenolite-hydrogen inclusion compound AsO·2H were performed in diamond anvil cells at high pressure and variable temperature down to 80 K. The experimental results were complemented by ab initio molecular dynamics simulations and phonon calculations. Observation of three hydrogen vibrons in AsO·2H is reported in the entire temperature and pressure range studied (up to 24 GPa). While the experiments performed with protium and deuterium at variable temperatures allowed for the assignment of two vibrons as Q(1) and Q(0) transitions of ortho and para spin isomers of hydrogen trapped in the inclusion compound, the origin of the third vibron could not be unequivocally established. Low-temperature spectra revealed that the lowest-frequency vibron is actually composed of two overlapping bands of A and T symmetries dominated by H stretching modes as predicted by our previous density functional theory calculations. We observed low-frequency modes of AsO·2H vibrations dominated by H "librations," which were missed in a previous study. A low-temperature fine structure was observed for the J = 0 → 2 and J = 1 → 3 manifolds of hydrogen trapped in AsO·2H, indicating the lifting of degeneracy due to an anisotropic environment. A non-spherical distribution was captured by molecular dynamics simulations, which revealed that the trajectory of H molecules is skewed along the crystallographic ⟨111⟩ direction. Last but not least, low-temperature synchrotron powder x-ray diffraction measurements on AsO·2H revealed that the bulk structure of the compound is preserved down to 5 K at 1.6 GPa.
在金刚石对顶砧池中对毒石 - 氢包合物AsO·2H进行了拉曼光谱测量，测量在高压和低至80 K的可变温度下进行。实验结果通过从头算分子动力学模拟和声子计算得到补充。报道了在整个研究的温度和压力范围（高达24 GPa）内AsO·2H中三个氢振动子的观测结果。虽然在可变温度下用氢和氘进行的实验能够将两个振动子归属于包合物中捕获的氢的正、仲自旋异构体的Q(1)和Q(0)跃迁，但第三个振动子的起源仍无法明确确定。低温光谱显示，最低频率的振动子实际上由两个重叠的A和T对称带组成，正如我们之前的密度泛函理论计算所预测的那样，它们主要由H伸缩模式主导。我们观察到AsO·2H振动的低频模式主要由H“摆动”主导，这在之前的研究中被忽略了。在AsO·2H中捕获的氢的J = 0 → 2和J = 1 → 3流形上观察到了低温精细结构，这表明由于各向异性环境导致简并解除。分子动力学模拟捕捉到了一种非球形分布，结果表明H分子的轨迹沿晶体学〈111〉方向发生了偏移。最后但同样重要的是，对AsO·2H进行的低温同步辐射粉末X射线衍射测量表明，该化合物的整体结构在1.6 GPa下可保持到5 K。
