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性结构安排的分子系统，其中伦敦色散力对能量偏好很重要。此外，考虑仅在分散相互作用足够强时才稳定的二聚体，如取代的六苯基乙烷二聚体，例如H原子之间的距离异常短。色散力的影响和数量都将在分子束实验中借助光谱技术进行研究，从而与量子化学方法相比产生振动频率和电子能量。一组系统进行研究是醚醇簇，其中的醇分子可以形成氢键的醚氧或一个π云，其中一个不同的醇侧链是能够控制的对接偏好，由于分散相互作用的变化量。或者，所连接的芳族醇分子可以与不同的烷基侧链相互作用，由分散相互作用的强度驱动。另一类研究的簇是不对称酮（包括受保护的氨基酸）与醇分子的聚集体。这里，醇分子的侧链相对于羰基氧原子的两个孤对的不同取向是可能的。所有的分析，无论是醚-醇和酮-醇集群，描述了近等能结构，即困难的情况下，理论预测之间的临界平衡，因为相对于能量的差异的不确定性可以在该地区的零点能量的差异。我们专注于我们的分子束调查的电子基态的中性和部分离子簇，但也对中性物种的激发态，通过应用各种组合的质量和异构体选择性IR/UV技术，以及受激拉曼/UV技术。此外，一个新的组合IR/拉曼/UV变量，这是重要的异构体选择性测量将被开发和应用。我们的实验研究将与互补光谱方法、理论和合成领域的其他工作组密切合作进行。合成组还为我们提供了特定的氘代或氟化化合物。这是一个总的目标，提供各种实验结果与理论预测相比。通过这一改进和发展的（新的）理论方法，可以实现，以得到一个更好的量化的伦敦色散，特别是包括电子激发态的分析。

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.