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

在化学系物理化学计划的这个项目中，加州理工学院的杰弗里·A·布莱克教授将对弱结合的范德华络合物和氢键络合物揭示的分子间作用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。这些络合物是在组成气体在高真空中的超音速膨胀中形成的，研究将集中在远红外区，那里是络合物的大部分分子间振动频率所在的地方。运行在微波、毫米和远红外区的混合激光光谱仪将被用来获得光谱，其分辨率适合于解析振动带的旋转、隧道和超精细结构。实验工作与计算和理论研究相结合，以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二阶、三阶和更高阶配合物，如苯-水、氨-水、氮-水和一氧化碳-水；氩-水，其中几个Ar原子和几个水分子形成一个络合物；由水与氟化氢、氯化氢、氰化氢和乙炔组成的二聚体络合物；以及较大尺寸的络合物，如甘氨酸-水和其他具有生物意义的络合物，如涉及氨基酸和嘌呤/嘧啶的络合物。分子间作用力的准确描述在化学和分子生物学中起着至关重要的作用。尽管对弱相互作用，即范德华效应，特别是氢键相互作用有长期的兴趣，但描述这些效应的可靠的定量数据很少。传统的获取分子间相互作用信息的方法是基于确定气体状态方程的维里展开式中的系数、谱线的压力展宽和其他经典性质。最近，分子束散射实验已经产生了有用的结果。分子束技术与高分辨率微波和激光光谱分析技术的耦合为获得由两个或两个以上强结合单体分子组成的弱结合络合物的最详细和准确的数据提供了工具。本项目所进行的研究将提供弱结合分子络合物的准确结构、寿命和其他动力学参数，以及关于其分子间势能的详细定量信息。这些信息不仅将使人们更好地了解物质的凝聚力，而且对环境和生物化学中具有实际意义的系统也是如此。

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.