Service de Chimie quantique et Photophysique, CP160∕09, Faculté des Sciences, Université Libre de Bruxelles, ave. F.D. Roosevelt, 50, B-1050 Brussels, Belgium.
J Chem Phys. 2011 Feb 14;134(6):064119. doi: 10.1063/1.3553203.
The equilibrium structure of acetylene (also named ethyne) has been reinvestigated to resolve the small discrepancies noted between different determinations. The size of the system as well as the large amount of available experimental data provides the quite unique opportunity to check the magnitude and relevance of various contributions to equilibrium structure as well as to verify the accuracy of experimental results. With respect to pure theoretical investigation, quantum-chemical calculations at the coupled-cluster level have been employed together with extrapolation to the basis set limit, consideration of higher excitations in the cluster operator, inclusion of core correlation effects as well as relativistic and diagonal Born-Oppenheimer corrections. In particular, it is found that the extrapolation to the complete basis set limit, the inclusion of higher excitations in the electronic-correlation treatment and the relativistic corrections are of the same order of magnitude. It also appears that a basis set as large as a core-valence quintuple-zeta set is required for accurately accounting for the inner-shell correlation contribution. From a pure experimental point of view, the equilibrium structure has been determined using very accurate rotational constants recently obtained by a "global analysis" (that is to say that all non-negligible interactions are explicitly included in the Hamiltonian matrix) of rovibrational spectra. Finally, a semi-experimental equilibrium structure (where the equilibrium rotational constants are obtained from the experimental ground state rotational constants and computed rovibrational corrections) has been obtained from the available experimental ground-state rotational constants for ten isotopic species corrected for computed vibrational corrections. Such a determination led to the revision of the ground-state rotational constants of two isotopologues, thus showing that structural determination is a good method to identify errors in experimental rotational constants. The three structures are found in a very good agreement, and our recommended values are r(CC) = 120.2958(7) pm and r(CH) = 106.164(1) pm.
乙炔（也称为乙块）的平衡结构已经重新进行了研究，以解决不同测定方法之间存在的微小差异。该体系的规模以及大量可用的实验数据为检查各种因素对平衡结构的贡献大小和相关性以及验证实验结果的准确性提供了非常独特的机会。在纯理论研究方面，采用了耦合簇水平的量子化学计算，并进行了基组极限外推、在簇算子中考虑更高的激发、包含核心相关效应以及相对论和对角 Born-Oppenheimer 修正。特别是，我们发现，基组极限外推、电子相关处理中更高激发的包含以及相对论修正的贡献处于相同的数量级。似乎需要像核心价五重-ζ基组这样大的基组，才能准确地考虑到内壳层相关贡献。从纯实验的角度来看，平衡结构是使用最近通过“全局分析”（即，所有不可忽略的相互作用都明确包含在哈密顿矩阵中）获得的非常精确的转动常数来确定的。最后，从十个同位素的实验基态转动常数中得到了一个半实验平衡结构（其中平衡转动常数从实验基态转动常数和计算的转动-振动修正中获得），并对计算的振动修正进行了修正。这种确定方法导致了两个同位素的基态转动常数的修订，从而表明结构确定是识别实验转动常数误差的好方法。这三种结构非常吻合，我们推荐的值为 r(CC) = 120.2958(7) pm 和 r(CH) = 106.164(1) pm。
