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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Ab Initio Study of the Most Stable C_4H_5 Isomers
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Ab Initio Study of the Most Stable C_4H_5 Isomers

机译：最稳定的C_4H_5异构体的从头算研究

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Ab initio calculations have been carried out on the lowest energy isomers of C_4H_5 to predict spectroscopic properties and relative stabilities. Geometry optimizations were carried out on stationary point conformations of seven configurational isomers at UHF, B3LYP, MP2, CISD, QCISD, MCSCF(7,7), and MCSCF(9,9) levels of theory. Single-point energies were evaluated at the MP4, CCSD(T), MCSCF(11,11), and multireference CISD levels, Disparities as large as 70 kJ mol~(-1) are found between relative energies predicted by single- and multireference methods for the same isomer. Comparison to experimental values suggests that the multireference methods inadequately model the relative correlation energy. Zero-point corrected relative energies (in kJ mol~(-1)) obtained at the QCISD level with a 6-311G(d,p) basis set are the following: 2-butyn-1-yl (0); 1-butyn-3-yl (10); 1,2-butadien-4-yl (13); cyclobuten-3-yl (17); 1,3-butadien-2-yl (50); 1,3-butadien-1-yl (59); and 1-butyn-4-yl (64). Relative energies calculated by multireference methods are higher, and decrease slowly as the active space size increases. Relative energies and hyperfine constants obtained at the QCISD level are in agreement with available experimental data and empirical estimates. Some of these isomers are candidates for relocalization, a phenomenon that results in predicted multiple minima and unusually flat vibrational potential energy surfaces for the isoelectronic C_3H_3O isomers. Of the present series of molecules, only 2-butyn-1-yl exhibits an especially flat bending potential along the appropriate somerization coordinate. Predicted vibrational transition frequencies and intensities, dipole moment components, Fermi contact hyperfine constants, and conformational potential energy curves are presented.
机译：已经对C_4H_5的最低能量异构体进行了从头算计算，以预测光谱性质和相对稳定性。在UHF，B3LYP，MP2，CISD，QCISD，MCSCF（7,7）和MCSCF（9,9）的理论水平上，对七个构型异构体的固定点构象进行了几何优化。在MP4，CCSD（T），MCSCF（11,11）和多参考CISD水平下评估了单点能量，发现单参考和多参考预测的相对能量之间的差异高达70 kJ mol〜（-1）。相同异构体的方法。与实验值的比较表明，多参考方法不足以对相对相关能量进行建模。具有6-311G（d，p）基组的QCISD水平获得的零点校正相对能量（以kJ mol〜（-1）为单位）为：2-丁炔-1-基（0）; 1-丁炔基-3-基（10）; 1,2-丁二烯-4-基（13）;环丁-3-基（17）; 1,3-丁二烯-2-基（50）; 1,3-丁二烯-1-基（59）;和1-butyn-4-yl（64）。通过多参考方法计算的相对能量较高，并且随着有效空间大小的增加而缓慢减小。在QCISD级别获得的相对能量和超精细常数与可用的实验数据和经验估计一致。这些异构体中的某些是重新定位的候选物，这种现象导致等电C_3H_3O异构体的预测的多个最小值和异常平坦的振动势能面。在当前的一系列分子中，只有2-丁炔基-1-基沿着适当的结化坐标显示出特别平坦的弯曲势。给出了预测的振动跃迁频率和强度，偶极矩分量，费米接触超精细常数以及构象势能曲线。

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