Dispersion interactions in isolated molecules and molecular aggregates analyzed by IR/UV and Raman/UV double resonance spectroscopy

在这个项目中，我们分析了各种具有竞争结构排列的分子系统，其中伦敦色散力对能量偏好是重要的。此外，只有在分散相互作用足够强的情况下才稳定的二聚体也被考虑在内，比如取代的六苯基乙烷二聚体，例如H原子之间的距离非常短。在分子束实验中，将借助光谱技术研究色散力的影响和数量，与量子化学方法相比，分子束实验产生的振动频率和电子能量。要研究的一组系统是醚-醇簇合物，其中醇分子可以与乙醚、氧或pi云形成氢键，并且由于分散相互作用的量的变化，不同的醇侧链能够控制对接偏好。或者，在分散相互作用强度的驱动下，附着的芳香醇分子可以与不同的烷基侧链相互作用。另一类被研究的簇是不对称酮(包括受保护的氨基酸)与酒精分子的聚集体。在这里，醇分子的侧链相对于两个孤对羰基氧原子的不同取向是可能的。所有的分析，包括醚醇和酮醇团簇，都描述了近等能结构之间的临界平衡，即提出了理论预测的困难情况，因为关于能量差的不确定性可能在零点能量差的区域内。我们的分子束研究集中在中性和部分离子团簇的电子基态，以及中性物种的激发态，应用各种组合的质量和同分异构体选择IR/UV技术以及受激拉曼/UV技术。此外，还将开发和应用一种新的红外/拉曼/紫外组合变体，这对异构体选择测量具有重要意义。我们的实验研究将在互补光谱方法、理论和合成领域与其他工作组密切合作进行。这些合成基团也为我们提供了专门的氢化或氟化化合物。它的总体目标是提供与理论预测相比较的各种实验结果。通过这种方法，可以改进和发展新的理论方法，以便更好地量化伦敦色散，特别是电子激发态的分析。

In this project we analyze a variety of molecular systems with competing structural arrangements in which London dispersion forces are important for the energetic preferences. Furthermore, dimers that are only stable if dispersion interactions are strong enough are considered, like substituted hexaphenyl ethane dimers with e.g. unusually short distances between H atoms. Both the influence and quantity of dispersion forces will be investigated with the help of spectroscopic techniques in molecular beam experiments yielding vibrational frequencies and electronic energies in comparison to quantum chemical methods. One set of systems to be investigated are ether–alcohol clusters in which the alcohol molecule can form a hydrogen bond to the ether oxygen or to a pi cloud and where a varying alcohol side-chain is able to control the docking preference due to changed amounts of dispersion interactions. Alternatively, an attached aromatic alcohol molecule can interact with different alkyl side chains, driven by the strength of dispersion interactions. A further class of investigated clusters are aggregates of asymmetric ketones (including protected amino acids) with alcohol molecules. Here, different orientations of the side-chains of the alcohol molecule with respect to the two lone pairs of the carbonyl oxygen atom are possible. All analyses, both for the ether–alcohol and ketone–alcohol clusters, describe a critical balance between nearly isoenergetic structures, i.e. difficult cases for theoretical predictions are presented, since the uncertainty with respect to energetic differences can be in the region of the difference of zero point energies. We focus our molecular beam investigations on the electronic ground state of neutral and partly ionic clusters, but also on the excited state of the neutral species by applying a variety of combined mass- and isomer-selective IR/UV techniques as well as stimulated Raman/UV techniques. Furthermore a new combined IR/Raman/UV variant which is important for isomer-selective measurements will be developed and applied. Our experimental investigations will be performed in close cooperation with other working groups in the field of complementary spectroscopic methods, theory, and synthesis. The synthetic groups also provide us with specifically deuterated or fluorinated compounds. It is a general aim to offer a variety of experimental results in comparison with theoretical predictions. By this an improvement and development of (new) theoretical methods can be achieved in order to get a better quantification of London dispersion, including especially the analysis of electronically excited states.