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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >An intricate molecule: Aluminum triiodide. molecular structure of AlI3 and Al2I6 from electron diffraction and computation
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An intricate molecule: Aluminum triiodide. molecular structure of AlI3 and Al2I6 from electron diffraction and computation

机译：复杂的分子：三碘化铝。电子衍射和计算的AlI3和Al2I6分子结构

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摘要

The molecular structure of aluminum triiodide was investigated in the gas phase by high-temperature gas-phase electron diffraction and high-level computations. The geometries of monomeric, AlI3, and dimeric, Al2I6, molecules were determined from two separate experiments carried out under carefully controlled conditions to prevent decomposition. This is the first experimental determination of the dimer structure by modern techniques. The computed geometrical parameters strongly depend on the applied methods and basis sets as well as on core-valence correlation effects. The electron diffraction thermal average bond length, r(g), of AlI3 at 700 K is 2.448(6) angstrom; while those of Al2I6 at 430 K are 2.456(6) angstrom (terminal) and 2.670(8) angstrom (bridging). The equilibrium geometry of the monomer molecule is planar with D-3h symmetry. The dimer molecule is extremely floppy, and it is difficult to determine the symmetry of its equilibrium geometry by computation, as it is sensitive to the applied methods. MP2 and CCSD calculations find the Al2I6 molecule puckered with C-2v symmetry (although with a very small barrier at planarity), while density functional methods give a structure with a planar central ring of D-2h symmetry. Comparison of the computed vibrational frequencies with the gas-phase experimental ones favors the D-2h symmetry structure.
机译：通过高温气相电子衍射和高级计算研究了气相中三碘化铝的分子结构。单体AlI3和二聚体Al2I6分子的几何结构是通过在仔细控制的条件下进行的两个单独实验确定的，以防止分解。这是通过现代技术对二聚体结构进行的首次实验测定。计算的几​​何参数在很大程度上取决于所应用的方法和基础集以及核心价相关效应。 AlI3在700 K时的电子衍射热平均键长r（g）为2.448（6）埃;而Al2I6在430 K时的电导率为2.456（6）埃（末端）和2.670（8）埃（桥接）。单体分子的平衡几何形状是平面的，具有D-3h对称性。二聚体分子非常松散，并且由于对所应用的方法敏感，因此难以通过计算确定其平衡几何形状的对称性。 MP2和CCSD计算发现Al2I6分子皱褶成C-2v对称性（尽管在平面性上具有很小的势垒），而密度泛函方法则给出了具有D-2h对称性的平面中心环的结构。计算出的振动频率与气相实验频率的比较有利于D-2h对称结构。

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