Wong Bryan M, Steeves Adam H, Field Robert W
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
J Phys Chem B. 2006 Sep 28;110(38):18912-20. doi: 10.1021/jp061924x.
A one-dimensional local bend model is used to describe the variation of electronic properties of acetylene in vibrational levels that embody large amplitude local motions on the S0 potential energy surface. Calculations performed at the CCSD(T) and MR-AQCC levels of theory predict an approximately linear dependence of the dipole moment on the number of quanta in either the local bending or local stretching excitation. In the local mode limit, one quantum of stretching excitation in one CH bond leads to an increase of 0.025 D in the dipole moment, and one quantum of bending vibration in the CCH angle leads to an increase of 0.068 D. The use of a one-dimensional model for the local bend is justified by comparison to the well-established polyad model which reveals a decoupling of the large amplitude bending from other degrees of freedom in the range of Nbend = 14-22. We find that the same one-dimensional large amplitude bending motion emerges from two profoundly different representations, a one-dimensional cut through an ab initio, seven-dimensional Hamiltonian and the three-dimensional (l = 0) pure-bending experimentally parametrized spectroscopic Hamiltonian.
一维局部弯曲模型用于描述乙炔在振动态下电子性质的变化，这些振动态体现了S0势能面上的大幅度局部运动。在CCSD(T)和MR - AQCC理论水平下进行的计算预测，偶极矩与局部弯曲或局部拉伸激发中的量子数近似呈线性关系。在局部模式极限下，一个CH键中的一个拉伸激发量子会导致偶极矩增加0.025 D，而CCH角中的一个弯曲振动量子会导致偶极矩增加0.068 D。通过与成熟的多组模型进行比较，证明了使用一维模型描述局部弯曲是合理的，该多组模型揭示了在Nbend = 14 - 22范围内，大幅度弯曲与其他自由度的解耦。我们发现，从两种截然不同的表示中出现了相同的一维大幅度弯曲运动，一种是通过从头算的七维哈密顿量的一维切面，另一种是三维（l = 0）纯弯曲实验参数化光谱哈密顿量。
