Conformational Analysis and Energetics of Cyclic and Open Chain Ketones, Ethers, and Hydrocarbons

在化学部实验物理化学计划的支持下，Tomas Baer将使用喷射冷却分子的共振增强多光子电离光谱(REMPI)来研究酮、醚和碳氢化合物等环和开链分子的紫外光谱和构象平衡。与温度相关的光谱数据将产生构象热差，可以与计算值进行比较。气相测量将与通过溶剂效应进行的溶液研究有关。超音速膨胀中的振动弛豫-异构化速率将使用主方程进行建模。相互作用能的准确测量将提供关于有机分子中烷基非键相互作用的性质和强度的有价值的信息。许多分子具有灵活的结构，在不破坏或建立任何连接原子的强化学键的情况下，原子的总位置可以显著变化。在分子的不同区域之间施加的许多比化学键弱得多的力可以强烈地影响分子中原子的整体排列。对于大分子系统(如生物分子)，这些小作用力的集体效应可以在决定分子的结构和功能行为方面发挥主导作用。这些研究将探索其中一些弱相互作用能量的性质。该项目的结果可能有助于完善用于计算预测大有机分子性质的数据库。

In this project supported by the Experimental Physical Chemistry Program of the Chemistry Division, Tomas Baer will use resonance enhanced multi-photon ionization spectroscopy (REMPI) of jet-cooled molecules to investigate the ultraviolet spectra and conformational equilibria of ring and open-chain molecules such as ketones, ethers, and hydrocarbons. Temperature-dependent spectral data will yield conformational enthalpy differences which can be compared with values from calculations. Gas-phase measurements will be related to solution studies via solvent effects. Vibrational relaxation-isomerization rates in the supersonic expansion will be modeled using the master equation. The accurate measurement of interaction energies will provide valuable information about the nature and strength of non-bonded interactions of alkyl groups in organic molecules. Many molecules have flexible structures, where the overall positions of atoms can vary significantly without breaking or making any of the strong chemical bonds that connect the atoms. The many forces exerted among different regions of a molecule that are much weaker than chemical bonds can strongly influence the overall arrangement of atoms in the molecule. For large molecular systems (such as biological molecules), the collective effect of these small forces can play a dominant role in determining the structure, and thus the functional behavior, of the molecule. These studies will explore the nature of some of these weak interaction energies. Results from this project could help to refine the data bases used for computational predictions of properties of large organic molecules.