Watrous Alexandria G, Fortenberry Ryan C
University of Mississippi, University, MS, USA.
Phys Chem Chem Phys. 2024 Aug 7;26(31):21260-21269. doi: 10.1039/d4cp02201g.
While -glyoxal may not be easily observable in astronomical sources through either IR or radioastronomy due to its symmetry, its conformer along with the -HCOCO epoxide isomer should be ready targets for astrochemical detection. The present quantum chemical study shows that not only are both molecular isomers strongly polar, they also have notable IR features and low isomerisation energies of 4.1 kcal mol and 10.7 kcal mol, respectively. These three isomers along with two other COH isomers have had their full set of fundamental vibrational frequencies and spectroscopic constants characterised herein. These isomers have previously been shown to occur in simulated astrophysical ices making them worthy targets of astronomical search. Furthermore, the hybrid quartic force field (QFF) approach utilized herein to produce the needed spectral data has a mean absolute percent error compared to the experimentally-available, gas phase fundamental vibrational frequencies of 0.6% and rotational constants to better than 0.1%. The hybrid QFF is defined from explicitly correlated coupled cluster theory at the singles, doubles, and perturbative triples level [CCSD(T)-F12b] including core electron correlation and a canonical CCSD(T) relativity correction for the harmonic (quadratic) terms in the QFF and simple CCSD(T)-F12b/cc-pVDZ energies for the cubic and quartic terms, the so-called "F12-TcCR+DZ QFF." This method is producing spectroscopically-accurate predictions for both fundamental vibrational frequencies and principal spectroscopic constants. Hence, the values computed in this work should be notably accurate and, hence, exceptionally useful to the spectroscopy and astrochemistry communities.
虽然由于乙二醛的对称性，通过红外或射电天文学在天体源中可能不容易观测到它，但其构象异构体以及-HCOCO环氧化物异构体应该是天体化学探测的理想目标。目前的量子化学研究表明，这两种分子异构体不仅极性很强，它们还具有显著的红外特征，异构化能分别低至4.1千卡/摩尔和10.7千卡/摩尔。这三种异构体以及另外两种COH异构体的全套基本振动频率和光谱常数在此得到了表征。这些异构体此前已被证明存在于模拟的天体物理冰中，这使得它们成为天文搜索的有价值目标。此外，本文中用于生成所需光谱数据的混合四次力场（QFF）方法，与实验可得的气相基本振动频率相比，平均绝对百分比误差为0.6%，与转动常数相比优于0.1%。混合QFF由单、双和微扰三激发水平的显式相关耦合簇理论[CCSD(T)-F12b]定义，包括核心电子相关，以及对QFF中谐波（二次）项的规范CCSD(T)相对论校正，对三次和四次项采用简单的CCSD(T)-F12b/cc-pVDZ能量，即所谓的“F12-TcCR+DZ QFF”。该方法对基本振动频率和主要光谱常数都能产生光谱精确的预测。因此，这项工作中计算出的值应该非常准确，对光谱学和天体化学领域格外有用。
