Theoretical Studies of Reaction Dynamics

斯图尔特·赖斯教授得到了理论和计算化学计划的资助，对化学动力学中的基本过程进行研究，目的是(I)改进激光控制化学反应中产物选择性的理论，以及(Ii)改进单分子反应速率理论。现有的激光控制量子系统演化的理论将扩展到非绝热反应的情况，并将通过引入反馈机制来改进该理论，该反馈机制在不精确了解系统哈密顿量中的所有分子参数的情况下塑造最佳激光场。基于现代非线性力学的单分子反应速率的描述将通过映射方法的推广而得到改进，这种映射方法将两个自由度系统的动力学精确表示为多个自由度系统。这些结果将被用于研究几种类型的单分子裂解和异构化反应。单分子反应速率经典理论的量子版本也将被开发出来。在整个化学发展过程中，人们一直在寻求实现对反应中产物形成的选择性控制。到目前为止，这种控制只能在宏观水平上完成，通过控制外部因素，如温度、压力、溶剂性质等。随着可调谐激光的出现，人们希望能够在微观水平上控制产品的选择性，并选择性地破坏分子中的单个键。人们很快发现，被分子吸收的能量不容易集中在单个键中，而是倾向于在整个分子中重新分配。然而，最近，激光选择化学的概念得到了重生，赖斯和其他人发展的理论表明，通过仔细选择指定形状的复杂激光脉冲序列，可以实现能量局部化。如果这一理论能够在实验上付诸实践，仍有可能实现化学反应微观选择性控制的目标。

Professor Stuart Rice is supported by a grant from the Theoretical and Computational Chemistry Program to perform studies of elementary processes in chemical dynamics for the purpose of (i) improving the theory of laser control of product selectivity in a chemical reaction, and (ii) improving the theory of unimolecular reaction rates. Existing theories of laser control of the evolution of a quantum system will be extended to the case of nonadiabatic reactions, and the theory will be improved by incorporation of a feedback mechanism that shapes the optimal laser field without precise knowledge of all of the molecular parameters in the system Hamiltonian. The description of unimolecular reaction rates based on modern nonlinear mechanics will be improved by extension of the mapping methods which provide an exact representation of the dynamics of systems with two degrees of freedom to systems with many degrees of freedom. The results will be used to study several types of unimolecular fragmentation and isomerization reactions. A quantum version of the classical theory of unimolecular reaction rates will also be developed. %%% The achievement of selective control of product formation in a reaction has been sought persistently throughout the evolution of chemistry. To date, such control has only been accomplished at the macroscopic level, by the manipulation of external factors such as temperature, pressure, solvent character, etc. With the advent of the tunable laser, it was hoped that product selectivity could be controlled at the microscopic level, and that individual bonds within a molecule could be selectively broken. It was very quickly found that energy absorbed by a molecule was not easily localized in individual bonds, but preferred to redistribute throughout the molecule. More recently, however, the concept of laser selective chemistry has had a rebirth, and theories developed by Rice and others have shown that energy could be localized by carefully choosing a complex sequence of laser pulses of prescribed shapes. If this theory can be put to practice experimentally, it may still be possible to realize the goal of microscopic selective control of chemical reactions.