Accurate Quantum Dynamics of Rare-Gas Heteroclusters and Hydrogen-Bonded Dimers

这项研究得到了NSF理论和计算的支持。 化学计划 严格的量子力学计算将 研究弱束缚系统的内部动力学， 特别是稀有气体异质团簇和氢键二聚体。 的 项目有三个主要组成部分。 (1)量子蒙特卡罗方法将 适用于由卤化氢分子组成的簇， 几个氩原子来研究溶剂-溶质相互作用对 能量学、结构和振动光谱。 (2)改进 将发展计算方法来处理振转态 四原子团簇的一个共价键。 大振幅 将明确地处理所有五个弱键的扭曲。 （三） 精确的量子计算将进行模式特定的 卤化氢二聚体的振动预解离动力学，以获得 预解离寿命和转动态的理论预测 所得单体片段的分布。 分子束技术和激光的十年进展 光谱学使得今天能够进行详细和高度 精确测量的相对能量的振动和 气相中非常小的分子团簇的旋转状态。 这些实验是重要的，高度准确的， 以及关于弱原子间力的详细信息，但进一步 需要进行理论工作以充分提取该信息。 的 目前的项目是一个理论研究的三个特殊类 簇的大小从4个原子到17个原子不等。 的显著差异 在这些团簇和具有相同数目的典型稳定分子之间， 是它们极度的松软。 发达的制药业 已经存在解决量子力学方程的方法， 典型分子的小振幅振动的运动。 的 较复杂的大振幅弱束缚运动理论 集群是当前研究的一个活跃领域。 这项工作是有动机的， 除了固有的科学好奇心之外， 关于弱分子间力的信息将用于随后的 大分子系统中分子运动的计算机模拟，例如 生物学感兴趣的分子和液体溶液中的分子。

This research is supported by the NSF theoretical and computational chemistry program. Rigorous quantum mechanical calculations will be carried out to study the internal dynamics of weakly bound systems, particularly, rare gas heteroclusters and hydrogen-bonded dimers. The project has three main components. (1) Quantum Monte Carlo methods will be applied to clusters consisting of a hydrogen halide molecule with several argon atoms to study the effects of solvent-solute interaction on energetics, structure, and the vibrational spectrum. (2) Improved computational methods will be developed for treating rovibrational states of four-atom clusters with one covalent bond. Large amplitude distortions of all five weak bonds will be treated explicitly. (3) Accurate quantum calculations will be carried out for mode-specific vibrational predissociation dynamics of hydrogen halide dimers to obtain theoretical predictions of predissociation lifetimes and rotational state distributions of the resulting monomer fragments. Advances during the past decade in molecular beam technology and laser spectroscopy have made it possible today to carry out detailed and highly precise measurements of the relative energies of vibrational and rotational states of very small molecular clusters in the gas phase. These experiments are potential sources of important, highly accurate, and detailed information about weak interatomic forces, but further theoretical work is required to fully extract this information. The present project is a theoretical study of three particular classes of clusters ranging in size from 4 to 17 atoms. The significant difference between these clusters and typical stable molecules with the same number of atoms are their extreme floppiness. Well developed mathematicals methods already exist for solving the quantum mechanical equations of motion for the small amplitude vibrations of typical molecules. The theory of the more compli cated, large amplitude, motion in weakly bound clusters is an active area of current research. This work is motivated, aside from inherent scientific curiosity, by the need for quantitative information about weak intermolecular forces to be used in subsequent computer simulations of molecular motion in large molecular systems, e.g. molecules of biological interest and molecules in liquid solution.