Owen Andrew N, Zdanovskaia Maria A, Esselman Brian J, Stanton John F, Woods R Claude, McMahon Robert J
Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States.
Quantum Theory Project, Departments of Physics and Chemistry, University of Florida, Gainesville, Florida 32611, United States.
J Phys Chem A. 2021 Sep 16;125(36):7976-7987. doi: 10.1021/acs.jpca.1c06187. Epub 2021 Sep 3.
A semi-experimental equilibrium structure () of pyridazine (-CHN) has been determined using the rotational spectra of 18 isotopologues. Spectroscopic constants of four isotopologues are reported for the first time (measured from 235 to 360 GHz), while spectroscopic constants for previously reported isotopologues are improved by extending the frequency coverage (measured from 130 to 375 GHz). The experimental values of the ground-state rotational constants (, , and ) from each isotopologue were converted to determinable constants (, , and ), which were then corrected for the effects of vibration-rotation interactions and electron-mass distributions using CCSD(T)/cc-pCVTZ calculations. The resultant for pyridazine determines bond distances to within 0.001 Å and bond angles within 0.04°, a reduction in the statistical uncertainties by at least a factor of two relative to the previously reported . The improvement in precision appears to be largely due to the use of higher-level theoretical calculations of the vibration-rotation and electron-mass effects, though the incorporation of the newly measured isotopologues ([4-H, 4-C]-, [4-H, 5-C]-, [4-H, 6-C]-, and [4,5-H, 4-C]-pyridazine) is partially responsible for the improved determination of the hydrogen-containing bond angles. The computed equilibrium structure () (CCSD(T)/cc-pCV5Z) and a "best theoretical estimate" of the equilibrium structure () both agree with the updated structure within the statistical experimental uncertainty (2σ) of each structural parameter.
已使用18种同位素异构体的转动光谱确定了哒嗪（-CHN）的半实验平衡结构（）。首次报告了四种同位素异构体的光谱常数（在235至360 GHz范围内测量），而通过扩展频率覆盖范围（在130至375 GHz范围内测量）改进了先前报告的同位素异构体的光谱常数。将每个同位素异构体的基态转动常数（、和）的实验值转换为可确定的常数（、和），然后使用CCSD(T)/cc-pCVTZ计算对振动-转动相互作用和电子质量分布的影响进行校正。由此得到的哒嗪的确定了键长在0.001 Å以内，键角在0.04°以内，相对于先前报告的，统计不确定性降低了至少两倍。精度的提高似乎主要归因于对振动-转动和电子质量效应使用了更高水平的理论计算，不过新测量的同位素异构体（[4-H, 4-C]-、[4-H, 5-C]-、[4-H, 6-C]-和[4,5-H, 4-C]-哒嗪）的纳入对含氢键角的改进测定也有部分贡献。计算得到的平衡结构（）（CCSD(T)/cc-pCV5Z）和平衡结构（）的“最佳理论估计”在每个结构参数的统计实验不确定性（2σ）范围内均与更新后的结构一致。
