Westbrook Brent R, Fortenberry Ryan C
Department of Chemistry & Biochemistry, University of Mississippi, University, Mississippi 38677-1848, United States.
J Phys Chem A. 2020 Apr 23;124(16):3191-3204. doi: 10.1021/acs.jpca.0c01609. Epub 2020 Apr 9.
The low-frequency vibrational fundamentals of inorganic oxides are readily modeled by heuristic scaling factors at fractions of the computational cost compared to explicit anharmonic frequency computations. Oxygen and the other elements in the present study are abundant in geochemical environments and have the potential to aggregate into minerals in planet-forming regions or in the remnants of supernovae. Explicit quartic force field computations at the CCSD(T)-F12b/cc-pVTZ-F12 level of theory generate scaling factors that accurately predict the anharmonic frequencies with an average error of less than 1.0 cm for both the metal-oxygen stretching frequencies and the torsion and antisymmetric stretching frequencies. Inclusion of hydrogen motions is less absolutely accurate but is similarly relatively predictive. The fundamental vibrational frequencies for the seven tetra-atomic inorganic oxides examined presently fall below 876 cm and most of the hydrogenated species do as well. Additionally, ν for the SiO dimer is shown to have an intensity of 562 km mol, with each of the other molecules having one or more frequencies with intensities greater than 80 km mol, again with most in the low-frequency infrared range. These intensities and the frequencies computed in the present study should assist in laboratory characterization and potential interstellar or circumstellar observation.
与显式非谐频率计算相比，无机氧化物的低频振动基频很容易用启发式缩放因子进行建模，计算成本仅为其几分之一。本研究中的氧和其他元素在地化环境中含量丰富，有可能在行星形成区域或超新星遗迹中聚集成矿物。在CCSD(T)-F12b/cc-pVTZ-F12理论水平上进行的显式四次力场计算生成了缩放因子，这些因子能准确预测非谐频率，对于金属-氧伸缩频率以及扭转和反对称伸缩频率，平均误差均小于1.0 cm⁻¹。包含氢运动的情况虽然绝对精度较低，但同样具有相对预测性。目前研究的七种四原子无机氧化物的基本振动频率低于876 cm⁻¹，大多数氢化物种也是如此。此外，SiO二聚体的ν显示强度为562 km mol⁻¹，其他每个分子都有一个或多个强度大于80 km mol⁻¹的频率，同样大多处于低频红外范围内。本研究计算出的这些强度和频率应有助于实验室表征以及潜在的星际或星周观测。
