A theoretical and experimental study of nitric oxide complexes.

涉及分子与未成对电子的分子间相互作用是从神经细胞信号传导到水氧化的现象的重要组成部分，并且有必要知道分子间电位，以便预测大气化学和气相化学反应（如燃烧）中分子的优选排列。然而，分子间势是很难获得的，并且具有未成对电子的分子使情况进一步复杂化，特别是当未成对电子可以占据两个或更多个具有相似能量的轨道时。在我们提出的工作中，我们将发展和评估我们认为最有希望计算具有未成对电子的分子间势的理论方法，并将该方法应用于涉及化学上重要的分子NO的相互作用，NO的未成对电子可以占据两个不同的π轨道。这些轨道在孤立的NO分子中能量相等（简并），但当其他分子在弱结合的分子复合物中与它相互作用时则不同。我们将使用一系列的实验方法来获得关于这些NO-X复合物的信息，其中X包括许多双原子分子、稀有气体原子和甲烷，并且NO分子将以几种不同的电子和自旋轨道状态制备。这项工作将涉及诺丁汉和牛津大学的研究小组之间的合作，他们在计算分子间势方面有经验，激发电子态的量子化学和货车范德华络合物的光谱学。这种专业知识的广度和深度，由与其他领先的研究小组和国家领先的超级计算机设施的合作支持，提供了在这个热门和令人兴奋的研究领域取得实质性进展的可能性。NO-X复合物的光谱学将使用微波光谱学来获得势能表面的低能区域的详细信息，并使用受激发射泵浦来获得基态电子态中复合物的高能振动和旋转状态的信息。这将为配合物的货车范德华伸缩运动和受阻转动运动提供新的信息，以及NO单体中的自旋-轨道相互作用与两个单体之间的货车范德华相互作用之间的相互作用。X复合物将使用超分子方法和新方法（包括分子间微扰理论和最大重叠理论）的组合进行计算。法分子间相互作用对空间简并度的分裂使得这些计算是非标准的并且非常具有挑战性，特别是对于激发态和多原子分子X。从分子间势出发，通过求解络合物核运动的薛定谔方程，包括由NO的不同自旋-轨道态与分子间势耦合产生的非玻恩-奥本海默效应，将预测理论旋转和振动光谱。实验与理论之间的相互作用将是至关重要的，因为新的理论方法可以通过它们再现实验数据的能力来评估，并且理论计算的结果将给出关于势能面的额外的、详细的信息，这些信息不能从实验中获得。从我们最近对NO-甲烷和NO-稀有气体复合物的A态的研究中，我们还可以预料，这些光谱将被证明是复杂的，难以分配。因此，理论计算对于理解实验数据是非常宝贵的。

Intermolecular interactions involving molecules with unpaired electrons are a crucial part of phenomena ranging from nerve cell signalling to water oxygenation, and it is necessary to know the intermolecular potential in order to predict the preferred alignment of molecules in atmospheric chemistry and in gas-phase chemical reactions such as combustion. However, intermolecular potentials are difficult to obtain, and molecules with unpaired electrons further complicate the situation, especially when an unpaired electron can occupy two or more orbitals with similar energies.In our proposed work, we shall develop and assess the theoretical methods that we believe are the most promising for calculating intermolecular potentials of molecules with unpaired electrons, and apply the methods to interactions involving the chemically important molecule NO, whose unpaired electron can occupy two different 'pi' orbitals. These orbitals are equal in energy (degenerate) in the isolated NO molecule, but not when other molecules interact with it in weakly bound molecular complexes. We shall use a range of experimental methods to obtain information about these NO-X complexes, where X includes a number of diatomic molecules, rare gas atoms, and methane, and the NO molecule will be prepared in several different electronic and spin-orbit states.The work will involve collaboration between research groups at the Universities of Nottingham and Oxford, with experience in the calculation of intermolecular potentials, quantum chemistry of excited electronic states, and spectroscopy of Van der Waals complexes. The breadth and depth of this expertise, supported by collaborations with other leading research groups and by nationally-leading supercomputer facilities, offers the likelihood of substantial progress in this topical and exciting area of research. The spectroscopy of NO-X complexes will use microwave spectroscopy to obtain detailed information on the low-energy regions of the potential energy surfaces, and stimulated emission pumping to obtain information on the higher-energy vibrational and rotational states of the complexes in the ground electronic state. This will provide new information on the Van der Waals stretching motion and the hindered rotational motion of the complexes, and on the interplay between the spin-orbit interaction in the NO monomer and the Van der Waals interaction between the two monomers.Intermolecular potentials for the NO-X complexes will be calculated using a combination of the supermolecule method and new methods including intermolecular perturbation theory and the Maximum Overlap Method. The splitting of the spatial degeneracy by the intermolecular interaction makes these calculations non-standard and very challenging, especially for excited states and for polyatomic molecules X. From the intermolecular potentials, theoretical rotational and vibrational spectra will be predicted by solving the Schrdinger equation for the nuclear motion of the complex, including the non-Born-Oppenheimer effects that arise from coupling of the different spin-orbit states of NO by the intermolecular potential.The interplay between experiment and theory will be crucial, because the new theoretical methods can be assessed by their ability to reproduce the experimental data, and the results of the theoretical calculations will give additional, detailed, information on the potential energy surfaces, which cannot be obtained from the experiments. It is also expected, from our recent work on NO-methane and on the A states of NO-rare gas complexes, that the spectra will prove to be complicated and difficult to assign. The theoretical calculations will therefore be invaluable in understanding the experimental data.