Lankhaar Boy, Groenenboom Gerrit C, van der Avoird Ad
Theoretical Chemistry, Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
J Chem Phys. 2016 Dec 28;145(24):244301. doi: 10.1063/1.4972004.
We present a rigorous derivation of the nuclear spin-rotation and spin-torsion coupling terms in the hyperfine Hamiltonian for molecules with internal rotation. Our formulas differ from the expressions derived by Heuvel and Dymanus [J. Mol. Spectrosc. 47, 363 (1973)], which these authors used and which were also applied recently by others to interpret experimental hyperfine spectra of such molecules. In the present work, our theoretical results are applied to methanol. We calculate the nuclear spin-spin magnetic dipole-dipole interactions and the nuclear contribution to the spin-torsion coupling vectors from the nuclear coordinates as functions of the internal rotation angle γ, compute the spin-rotation coupling tensors by ab initio electronic structure methods also as functions of γ, and obtain the missing parameters for the electronic contribution to the spin-torsion coupling from a fit to measured spectra. The resulting hyperfine Hamiltonian is then used to compute hyperfine transition frequencies and intensities for twelve torsion-rotation transitions in methanol. With the use of the ab initio calculated spin-rotation coupling parameters without any modification, and physically reasonable values for the spin-torsion coupling parameters from the fit, we find good agreement with all of the measured spectra.
我们给出了具有内旋转的分子的超精细哈密顿量中核自旋 - 旋转和自旋 - 扭转耦合项的严格推导。我们的公式与赫维尔（Heuvel）和戴曼努斯（Dymanus）[《分子光谱学杂志》47, 363 (1973)]推导的表达式不同，这些作者使用的表达式以及最近其他人用于解释此类分子的实验超精细光谱的表达式。在本工作中，我们将理论结果应用于甲醇。我们计算核自旋 - 自旋磁偶极 - 偶极相互作用以及核坐标对自旋 - 扭转耦合矢量的贡献作为内旋转角γ的函数，通过从头算电子结构方法计算自旋 - 旋转耦合张量同样作为γ的函数，并通过拟合测量光谱获得自旋 - 扭转耦合的电子贡献的缺失参数。然后，所得的超精细哈密顿量用于计算甲醇中十二个扭转 - 旋转跃迁中的超精细跃迁频率和强度。使用未经任何修改的从头算计算的自旋 - 旋转耦合参数，以及拟合得到的自旋 - 扭转耦合参数的合理物理值，我们发现与所有测量光谱都有很好的一致性。
