Mackenzie Rebecca B, Dewberry Christopher T, Cornelius Ryan D, Smith C J, Leopold Kenneth R
Department of Chemistry, University of Minnesota , 207 Pleasant Street, SE, Minneapolis, Minnesota 55455, United States.
Department of Chemistry and Biochemistry, Kettering University , 1700 University Avenue, Flint, Michigan 48504, United States.
J Phys Chem A. 2017 Feb 2;121(4):855-860. doi: 10.1021/acs.jpca.6b11255. Epub 2017 Jan 20.
Aqueous pyridine plays an important role in a variety of catalytic processes aimed at harnessing solar energy. In this work, the pyridine-water interaction is studied by microwave spectroscopy and density functional theory calculations. Water forms a hydrogen bond to the nitrogen with the oxygen tilted slightly toward either of the ortho-hydrogens of the pyridine, and a tunneling motion involving in-plane rocking of the water interconverts the resulting equivalent structures. A pair of tunneling states with severely perturbed rotational spectra is identified and their energy separation, ΔE, is inferred from the perturbations and confirmed by direct measurement. Curiously, values of ΔE are 10404.45 and 13566.94 MHz for the HO and DO complexes, respectively, revealing an inverted isotope effect upon deuteration. Small splittings in some transitions suggest an additional internal motion making this complex an interesting challenge for theoretical treatments of large amplitude motion. The results underscore the significant effect of the ortho-hydrogens on the intermolecular interaction of pyridine.
含水吡啶在各种旨在利用太阳能的催化过程中起着重要作用。在这项工作中，通过微波光谱和密度泛函理论计算研究了吡啶 - 水的相互作用。水与氮形成氢键，氧略微向吡啶的邻位氢之一倾斜，并且涉及水的面内摇摆的隧穿运动使所得的等效结构相互转换。识别出一对具有严重扰动的旋转光谱的隧穿态，并从扰动中推断出它们的能量间隔ΔE，并通过直接测量得到证实。奇怪的是，HO和DO配合物的ΔE值分别为10404.45和13566.94 MHz，揭示了氘化时的同位素效应反转。一些跃迁中的小分裂表明存在额外的内部运动，使得该配合物成为大振幅运动理论处理的一个有趣挑战。结果强调了邻位氢对吡啶分子间相互作用的显著影响。
