School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, United Kingdom.
J Phys Chem A. 2010 Sep 2;114(34):9309-18. doi: 10.1021/jp104498n.
Infrared (IR) spectra in the gas phase are reported for CF(2)=CHD and CF(2)=CD(2) in the region 350-4000 cm(-1). Ab initio calculations of an harmonic force-field and anharmonicity constants have been made with an MP2/aug-cc-pVTZ model. These enable a number of Fermi resonances in each species to be analyzed and a complete set of "observed" harmonic frequencies to be derived. The latter are combined with similar data for CF(2)=CH(2) in a scaling of the model harmonic force field to both anharmonic and harmonic frequencies. Inspection of the scale factors reveals minor defects of the model, evident in the out-of-plane wagging modes and in the CF stretch/CF stretch interaction force constant. Fermi resonance treatments involved in all isotopomers studied are compatible with the overall force-field refinement results. The treatment leaves a small anomaly in the (13)C shift on nu(1). Improved microwave spectra are reported for five isotopic species, and a semiexperimental equilibrium structure for F(2)C=CH(2) is determined and compared favorably with the structure obtained from new high-level ab initio calculations. Centrifugal distortion constants are predicted for the five isotopic species, and those for F(2)C=CH(2) are compared with values fit to microwave spectra.
报道了 CF(2)=CHD 和 CF(2)=CD(2)在 350-4000 cm(-1) 范围内的气相红外光谱。采用 MP2/aug-cc-pVTZ 模型进行了谐振动力场和非谐常数的从头算计算。这些计算能够分析每种物质中的一些费米共振,并推导出一套完整的“观察”谐振动频率。将后者与 CF(2)=CH(2)的类似数据结合起来,对模型谐振动力场进行了非谐和谐振动频率的缩放。对缩放因子的检查揭示了模型的一些小缺陷,这些缺陷在面外摇摆模式和 CF 伸缩/CF 伸缩相互作用力常数中表现明显。在所研究的所有同位素中,费米共振处理与整体力场改进结果兼容。该处理在 ν(1)上的 (13)C 位移上留下一个小异常。报道了五个同位素的改进微波光谱,并确定了 F(2)C=CH(2)的半实验平衡结构,并与从新的高精度从头算计算获得的结构进行了很好的比较。预测了五个同位素的离心畸变常数,并将 F(2)C=CH(2)的常数与拟合微波光谱的常数进行了比较。