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首页> 外文期刊>Spectrochimica acta, Part A. Molecular and biomolecular spectroscopy >A comparative study of vibrational anharmonicity in the bihalide anions XHX~-: X=F, Cl, Br
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A comparative study of vibrational anharmonicity in the bihalide anions XHX~-: X=F, Cl, Br

机译：双卤化物阴离子XHX〜-的振动非谐性比较研究：X = F，Cl，Br

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摘要

MP2/6-31+G(d, p), MP2/aug'-cc-p-VTZ, CCSD/aug'-cc-pVTZ and CCSD(T)/aug'-cc-pVTZ calculations were performed for the bihalide ions XHX~-, for X=F, Cl and Br. Equilibrium geometries were determined and harmonic vibrational frequencies computed. At each level of theory potential surfaces were generated in the two X-H bondlengths and a model two-dimensional vibrational problem was solved to obtain anharmonic symmetric (v_1) and asymmetric (v_3) stretching frequencies. The computed harmonic frequencies are very dependent on the level of theory used, a consequence of the difficulties in describing the various XHX~- potential energy surfaces in the vicinity of the global minimum. Vibrational averaging in the anharmonic calculations results in anharmonic frequencies which exhibit much less variation with level of theory. Improved results are obtained even at the lowest level of theory, MP2/6-31+G(d, p). Anharmonic calculations on the CCSD(T)/aug'-cc-pVTZ potential energy surfaces reproduce the experimentally observed frequencies for both the XHX~- complexes and their deuterated analogs, XDX~-. Anharmonic effects become increasingly important along the series F, Cl and Br and anharmonic frequencies for the fundamental vibrations and combination bands are necessary for understanding and assigning the experimental spectra of these complexes.
机译：对二卤化物进行了MP2 / 6-31 + G（d，p），MP2 / aug'-cc-p-VTZ，CCSD / aug'-cc-pVTZ和CCSD（T）/ aug'-cc-pVTZ计算离子XHX〜-，对于X = F，Cl和Br。确定平衡几何形状，并计算谐波振动频率。在理论的每个水平上，均会在两个X-H键长中生成潜在的表面，并解决了模型二维振动问题，从而获得了非对称对称（v_1）和非对称（v_3）拉伸频率。计算的谐波频率非常依赖于所使用的理论水平，这是描述全局最小值附近各种XHX〜-势能面的困难的结果。非谐计算中的振动平均导致非谐频率随理论水平的变化小得多。即使在最低的理论水平MP2 / 6-31 + G（d，p），也可以获得改进的结果。在CCSD（T）/ aug'-cc-pVTZ势能面上的非谐计算可重现XHX〜-配合物及其氘代类似物XDX〜-的实验观测频率。沿着F，Cl和Br系列，非谐效应变得越来越重要，对于理解和分配这些配合物的实验光谱，基本振动和组合频带的非谐频率是必不可少的。

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