Vázquez J., Demaison J., López-González J. J., Boggs James E., Rudolph H. D.
Department of Analytical and Physical Chemistry, University of Jaén, Jaén, 23071, Spain
J Mol Spectrosc. 2001 Jun;207(2):224-237. doi: 10.1006/jmsp.2001.8335.
The equilibrium structure of 1,2,5-oxadiazole has been calculated ab initio at the CCSD(T) level using a polarized valence quadruple zeta basis set. The harmonic force field has also been calculated at the MP2/cc-pVTZ, B3LYP/6-311++G(3df, 2pd), and B3LYP/cc-pVQZ levels. These force fields have been subsequently scaled and further refined by fitting them to the experimental values of the vibrational fundamentals of three isotopomers and the centrifugal distortion constants of the parent molecule. The specific refinement of those scaled force constants particularly sensitive to the experimental data set was decisive for obtaining a more reliable harmonic potential. The resulting force fields are presented and used, together with the ground state rotational constants, to calculate an r(z) structure. The experimental r(0), r(s), and r(m) structures have also been determined. The different results have been compared and it is concluded that the ab initio structure is a good approximation of the equilibrium structure. It is also shown that the magnetic correction is not negligible, particularly for the inertial defect. Another interesting conclusion is that the anharmonicity of the C-H stretching might be unusually small. Copyright 2001 Academic Press.
已使用极化价四重zeta基组在CCSD(T)水平从头计算了1,2,5 - 恶二唑的平衡结构。还在MP2/cc - pVTZ、B3LYP/6 - 311++G(3df, 2pd)和B3LYP/cc - pVQZ水平计算了谐性力场。随后通过将这些力场与三种同位素异构体的振动基频实验值以及母体分子的离心畸变常数拟合，对其进行了缩放和进一步优化。对那些对实验数据集特别敏感的缩放力常数进行的特定优化对于获得更可靠的谐性势起了决定性作用。给出了所得的力场，并将其与基态转动常数一起用于计算r(z)结构。还确定了实验性的r(0)、r(s)和r(m)结构。对不同结果进行了比较，得出从头计算结构是平衡结构的良好近似这一结论。还表明磁校正不可忽略，特别是对于惯性缺陷。另一个有趣的结论是C - H伸缩振动的非谐性可能异常小。版权所有2001年学术出版社。
