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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 on Spectroscopic Properties of GdF_3 and GdCl_3
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Ab Initio Study on Spectroscopic Properties of GdF_3 and GdCl_3

机译：从头算研究GdF_3和GdCl_3的光谱性质

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The geometry and vibrational frequencies of the GdX_3 (X = F and Cl) molecules have been analyzed at the ab initio level with extended basis sets, employing relativistic effective core potential, and evaluating electronic correlation by means of second-order perturbative (MP2) and coupled cluster (CCSD and CCSD(T)) methods. Anharmonicities, temperature, and inert-gas matrix effects have been explicitly included. The MP2, CCSD, and CCSD(T) calculations on the systems in the gas phase indicate a trigonal planar equilibrium structure for GdCl3 and a quasiplanar geometry for GdF3. Vibrationally averaged bond angle, evaluated by means of a simple one-dimensional treatment, is considerably smaller than the equilibrium value and both molecules have a pyramidal thermal average structure, in agreement with recent electron diffraction measurements. The theoretical estimate of Gd-X bond lengths depends on both the electronic correlation treatment and the basis set quality, thus indicating the desirability of high-level calculations. Experimental and theoretical comparison becomes quantitative after including thermal correction. Anharmonic vibrational frequencies have been computed through the vibrational self-consistent field method followed by the second-order perturbation correction. For both gadolinium trihalides, the 2 out-of-plane bending potential shows a huge "negative" anharmonic form and hot bands fall at considerably higher energies than the fundamental one. Although the anharmonicities for the remaining modes are small, they are important for a correct interpretation of experimental IR spectra. The inert-gas matrix interactions, modeled by coordination of one and two inert-gas molecules GdX_3·IGm (IG = Ne, Ar, Xe, and N_2; m = 1 and 2), are substantial and GdX_3 structures strongly depend on the number of coordinating molecules and on the interaction strength. As a consequence, all normal-mode frequencies slightly diminish as GdX3- -IG_m interactions grow, while the 2 out-of-plane bending frequency significantly increases.
机译：GdX_3（X = F和Cl）分子的几何形状和振动频率已在从头算的水平上使用扩展的基集进行了分析，采用相对论有效核心电位，并通过二阶微扰（MP2）和耦合聚类（CCSD和CCSD（T））方法。非谐性，温度和惰性气体基质效应已明确包括在内。在气相系统上的MP2，CCSD和CCSD（T）计算表明GdCl3为三角形平面平衡结构，GdF3为准平面几何结构。通过简单的一维处理评估的振动平均键角大大小于平衡值，并且与最近的电子衍射测量结果一致，两个分子均具有金字塔热平均结构。 Gd-X键长的理论估计值取决于电子相关性处理和基集质量，因此表明需要进行高级计算。包括热校正后，实验和理论比较变得定量。通过振动自洽场方法，然后进行二阶扰动校正，计算出非谐振动频率。对于这两种三卤化ides，其2个面外弯曲势均显示出巨大的“负”非谐形式，并且热带的能量远低于基带。尽管其余模式的非谐性很小，但它们对于正确解释实验红外光谱很重要。通过一个和两个惰性气体分子GdX_3·IGm（IG = Ne，Ar，Xe和N_2; m = 1和2）的配位关系建模的惰性气体基体相互作用非常重要，GdX_3结构强烈取决于数量分子和相互作用强度的关系。结果，随着GdX3- -IG_m相互作用的增加，所有正常模式的频率都会略微降低，而2个平面外弯曲频率会显着增加。

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