Accurate equilibrium structures of some challenging molecules: FNO, ClNO, HONO, FNO2, and N2O

IF 1.4 4区 物理与天体物理 Q4 PHYSICS, ATOMIC, MOLECULAR & CHEMICAL Journal of Molecular Spectroscopy Pub Date : 2023-04-01 DOI:10.1016/j.jms.2023.111788
Jean Demaison , Jacques Liévin , Natalja Vogt
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引用次数: 1

Abstract

It is sometimes difficult to determine the structure of some molecules because the optimization using standard ab initio methods (coupled-cluster with single, double, and perturbative triples [CCSD(T)] level) does not give the correct result and the experimental and semiexperimental methods are not accurate because the system of normal equations of the least-squares method is ill-conditioned. In such a case, it may be still possible to derive an accurate equilibrium structure in the following way: the experimental rotational constants are compared to those obtained at the CCSD(T) level, the latter being corrected to take into account the rovibrational correction (and, if necessary, the electronic correction). Extrapolating (or interpolating) the rotational constants calculated with different basis sets (e.g. cc-pwCVTZ and cc-pwCVQZ) towards the experimental values as a function of the bond lengths and angles permits to obtain an accurate equilibrium structure. This method is first tested on two molecules for which the multireference effects are important: O3 and HOON. It is then, applied to molecules with a weak N–X bond (HONO, FNO, ClNO, FNO2, and N2O) for which the single reference CCSD(T) method gives bonds that are too short. The results are compared to the experimental and semiexperimental equilibrium structures. As a further check, the structure of ClNO is calculated at the CCSDTQ level and the structures of FNO and ClNO are calculated at the MRCI-F12 level. From a comparison of the different results, it appears that the accuracy of the proposed method is better than 0.002 Å for the bond lengths and 0.3° for the angles.

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一些具有挑战性的分子:FNO, ClNO, HONO, FNO2和N2O的精确平衡结构
一些分子的结构有时难以确定,因为使用标准的初始化方法(单、双和摄动三元组[CCSD(T)]水平的耦合簇)进行优化不能给出正确的结果,而实验和半实验方法由于最小二乘法的正方程系统是病态的而不准确。在这种情况下,仍有可能通过以下方式推导出精确的平衡结构:将实验旋转常数与在CCSD(T)水平上获得的旋转常数进行比较,并对后者进行校正,以考虑旋转振动校正(必要时,还有电子校正)。将不同基集(例如cc-pwCVTZ和cc-pwCVQZ)计算的旋转常数作为键长和角度的函数,向实验值外推(或内插),可以获得精确的平衡结构。该方法首先在两个多参比效应重要的分子上进行了测试:O3和HOON。然后,将其应用于具有弱N-X键的分子(HONO, FNO, ClNO, FNO2和N2O),对于这些分子,单一参考CCSD(T)方法给出的键太短。结果与实验和半实验平衡结构进行了比较。为了进一步检验,在CCSDTQ水平计算ClNO的结构,在MRCI-F12水平计算FNO和ClNO的结构。从不同结果的比较中可以看出,该方法的键长精度优于0.002 Å,键角精度优于0.3°。
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来源期刊
CiteScore
2.70
自引率
21.40%
发文量
94
审稿时长
29 days
期刊介绍: The Journal of Molecular Spectroscopy presents experimental and theoretical articles on all subjects relevant to molecular spectroscopy and its modern applications. An international medium for the publication of some of the most significant research in the field, the Journal of Molecular Spectroscopy is an invaluable resource for astrophysicists, chemists, physicists, engineers, and others involved in molecular spectroscopy research and practice.
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