High Resolution Vibration - Rotation - Tunneling Spectroscopy of Weakly Bound Complexes

在化学学部物理化学项目中，来自加州理工学院的Geoffrey A. Blake教授将对弱键（即范德华和氢键）配合物所揭示的分子间力进行详细的光谱研究。这些研究将包括实验、计算和理论研究。这些配合物是在组成气体进入高真空的超音速膨胀中形成的，研究将集中在远红外区域，因为这些配合物的大多数分子间振动频率都位于远红外区域。在微波、毫米和远红外区域工作的混合激光光谱仪将用于获得光谱，其分辨率适合于解析振动带的旋转、隧道和超精细结构。将实验努力与计算和理论研究相结合，从实验数据中提取可靠的分子间势能面。要研究的系统包括由单体分子组成的双、三和高阶配合物，如苯-水、氨-水、氮-水和一氧化碳-水；氩-水，其中几个氩原子和几个水分子形成络合物；由水与氟化氢、氯化氢、氰化氢和乙炔组成的二聚物；更大的复合物，如甘氨酸-水和其他生物重要性，如涉及氨基酸和嘌呤/嘧啶的复合物。分子间作用力的准确描述在化学和分子生物学中起着关键作用。尽管对弱相互作用，即范德华作用，特别是氢键相互作用有长期的兴趣，但缺乏可靠的定量数据来描述这些效应。获取分子间相互作用信息的传统方法是基于气体状态方程的维里展开系数的确定、谱线的压力展宽和其他经典性质。最近，分子束散射实验产生了有用的结果。分子束技术与高分辨率微波和激光光谱技术的耦合提供了工具，通过这些工具可以获得由两个或多个单独的强结合单体分子组成的弱结合配合物的最详细和精确的数据。本项目所进行的研究将有助于提供弱结合分子复合物的精确结构、寿命和其他动力学参数，以及它们的分子间势能的详细定量信息。这些信息不仅会使我们更好地理解一般物质的内聚力，而且对那些在环境和生物化学中具有实际重要性的系统也有帮助。

In this project in the Physical Chemistry program of the Chemistry Division, Prof. Geoffrey A. Blake of the California Institute of Technology will engage in detailed spectroscopic studies of intermolecular forces as revealed by weakly bound, i.e., van der Waals and hydrogen-bonded, complexes. These studies will encompass experimental, computational, and theoretical investigations. The complexes are formed in supersonic expansions of the component gases into a high vacuum, and the studies will focus on the far infrared region where most of the telltale intermolecular vibrational frequencies of the complexes are located. Hybrid laser spectrometers that operate throughout the microwave, millimeter, and far-infrared regions will be used to obtain the spectra, with resolution appropriate to resolve the rotational, tunneling, and hyperfine structures of the vibrational bands. The experimental efforts are coupled to computational and theoretical studies to extract from the experimental data reliable intermolecular potential energy surfaces. Systems to be investigated include bi-, tri, and higher-order complexes composed of monomer molecules, such as benzene-water, ammonia-water, nitrogen-water, and carbon monoxide-water; argon-water in which the several argon atoms and several water molecules form a complex; dimer complexes composed of water with hygrogen fluoride, hydrogen chloride, hydrogen cyanide, and acetylene; and larger size complexes such as glycine-water and others of biological importance such as those involving amino acids and purines/pyrimidenes. Accurate descriptions of intermolecular forces play a pivotal role in chemistry and molecular biology. Despite long term interests in the weak, i.e., van der Waals and, in particular, hydrogen-bonded, interactions there is a paucity of reliable quantitative data that describe these effects. Traditional methods for obtaining information on the intermolecular interactions were based on the determination of the coefficients in the virial expansion of the equation of state of a gas, pressure broadening of spectral lines, and other classical properties. More recently molecular beam scattering experiments have yielded useful results. The couplings of molecular beam techniques with those of high resolution microwave and laser spectroscopies have provided tools by means of which the most detailed and exact data on weakly bound complexes composed of two or more individually strongly bound monomer molecules are obtained. The investigations pursued in this project will contribute accurate structures, lifetimes and other dynamical parameters of weakly bound molecular complexes as well as detailed quantitative information on their intermolecular potential energies. This information will lead not only to a better understanding about the cohesion of matter in general, but also for those systems that are of practical importance in environmental and biological chemistry.