Spectra, Dynamics, and Intermolecular Forces in Small Molecules and Clusters

小分子和团簇中的光谱、动力学和分子间力

• 批准号: RGPIN-2014-03929
• 负责人: LeRoy, Robert
• 金额: $ 3.13万
• 依托单位: University of Waterloo
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=632423
• 关键词: Spectra; Dynamics; Intermolecular; Forces; Small

Knowledge of the intermolecular forces or interaction energies within and between molecules is essential for understanding and making predictions about properties of systems ranging from simple dimers to dilute gases to bulk liquids or to solids. Developing and applying methods for determining and representing such interactions, and utilizing such information to study simple molecules, both isolated and in clusters or condensed phase environments, is the central theme of this proposal.1) Diatomic Molecule Modelling, Data Analyses, and Computational Methods.This project is centred around the development and application of the 'direct potential fit' method of data analysis, in which a comparison of experimental spectra with the results of an exact quantum simulation based on a flexible analytic model potential energy function is used to optimize parameters defining both the model potential function and the atomic mass-dependent Born-Oppenheimer breakdown correction functions required to make the data for different isotopologues consistent with one another. This approach was first introduced in our (1974) treatment of three-dimensional atom-diatom Van der Waals molecules, and its applications to diatomics have been developed over the past 20 years in a number of laboratories around the world. It provides more fundamental physical information, and yields much better extrapolation and interpolation predictions than do conventional 'parameter-fit' analyses. However, the limitations of some of the potential forms used and the complexity of the method have inhibited its general adoption. Our work has included the development of a better way of solving the radial Schroedinger equation that allows levels lying extremely close to dissociation to be located and treated just as easily as levels lying deep in a potential well. It has also included the development and testing of improved potential function models that incorporate the correct theoretically-known long-range behaviour. Planned work includes an extension of this model to allow it to better deal with non-standard 'potential shelf', double-minimum or barrier behaviour. 2) Simulations of Dynamics and Vibrational Shifts in Molecular Clusters and Matrices.The most discriminating experimental probe of the physical properties and behaviours of molecular ('Van der Waals') clusters are the spectra of chromophores seeded into or onto the cluster. However, to exploit fully the experimental work requires a quantitative understanding of how the spectroscopic properties of the chromophore molecule are affected by its surroundings. Understanding and predicting the vibrational frequency shifts of molecules trapped within or on the surface of solids is a similar problem, since both are governed by the same types of microscopic intermolecular interaction and frequency-shift mechanisms. Quantitative understanding of such shifts would facilitate probing local order in and on the surface of materials, determining the phase behaviour (liquid-like vs. solid-like) of finite molecular clusters, and examining solvation behaviours in cluster-type systems. Our previous work included the development of a successful model for quantitative prediction of the splitting and shifting of IR spectra of a certain type of chromophore in a cluster environment; it showed that such spectra could provide distinct signatures for cluster size, structure and phase behaviour. We are now applying path-integral quantum Monte Carlo methods to simulate the properties and spectroscopic signatures of infrared chromophores in molecular clusters, and have found that they provide sharp tests of subtleties of the interactions and the nature of the dynamical behaviour and possible presence of superfluidity.

分子内部和分子之间的分子间力或相互作用能的知识对于理解和预测从简单的二聚体到稀气体到散装液体或固体的系统性质是必不可少的。发展和应用确定和表示这种相互作用的方法，并利用这种信息来研究简单的分子，包括孤立的和在团簇或凝聚相环境中的分子，是本项目的中心主题。1）双原子分子建模，数据分析和计算方法。本项目围绕数据分析的“直接势拟合”方法的发展和应用，其中实验光谱与基于灵活的分析模型势能函数的精确量子模拟的结果的比较用于优化定义模型势能函数和原子质量相关的Born-Oppenheimer击穿校正函数两者的参数，所述模型势能函数和原子质量相关的Born-Oppenheimer击穿校正函数需要使不同同位素体的数据彼此一致。这种方法首先在我们（1974）对三维原子-硅藻货车范德华分子的处理中引入，并且在过去的20年中，它在生物化学中的应用已经在世界各地的许多实验室中得到了发展。它提供了更多的基本物理信息，并产生更好的外推和插值预测比传统的“参数拟合”分析。然而，所使用的一些潜在形式的局限性和该方法的复杂性阻碍了其普遍采用。我们的工作包括发展一种更好的方法来求解径向薛定谔方程，这种方法可以使非常接近离解的能级像深埋在势阱中的能级一样容易定位和处理。它还包括开发和测试改进的潜在功能模型，这些模型纳入了理论上已知的正确长期行为。计划中的工作包括对该模型的扩展，使其能够更好地处理非标准的“潜在货架”、双最小值或障碍行为。2)分子团簇和基质中的动力学和振动位移的模拟研究分子团簇（“范德华”）的物理性质和行为的最有鉴别力的实验探针是在团簇中或团簇上播种的发色团的光谱。然而，为了充分利用实验工作，需要定量了解发色团分子的光谱特性如何受到其周围环境的影响。理解和预测被困在固体内部或表面上的分子的振动频率偏移是一个类似的问题，因为两者都由相同类型的微观分子间相互作用和频率偏移机制控制。定量了解这种变化将有助于探测材料表面和内部的局部秩序，确定有限分子团簇的相行为（类液体与类固体），并检查团簇型系统中的溶剂化行为。我们以前的工作包括开发一个成功的模型，用于定量预测在簇环境中的某种类型的发色团的红外光谱的分裂和移位;它表明，这样的光谱可以提供不同的签名簇的大小，结构和相行为。我们现在正在应用路径积分量子蒙特卡罗方法来模拟分子团中红外发色团的性质和光谱特征，并发现它们提供了对相互作用的微妙之处、动力学行为的本质以及可能存在的性质的尖锐测试。超流。