Studies of the Control of Quantum Dynamics

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Stuart Rice is supported by a grant from the Theoretical and Computational Chemistry Program to continue his work on the theory of control of the evolution of quantum many body systems with applications to the selective enhancement of products of a chemical reaction. Four areas of study will be pursued: 1) refinements and extensions of the Kobrak-Rice photoselective adiabatic passage scheme; 2) the accuracy of reduced dynamical descriptions of an excited molecule; 3) the control of the evolution of a molecule embedded in a solvent; and 4) the possible existence of a fundamental limit to the extent of control of quantum dynamics that is attainable. Much of the theoretical approach to coherent control will be developed as an extension to the generalized Stimulated Raman Adiabatic Passage (StiRAP) process for control of product selectivity in a reaction.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.