Control of Selectivity of Chemical Reaction Via Control of Wave Packet Evolution

摘要

Is it possible, by control of the nature of the excitation process, to control the selectivity of a chemical reaction. Previous attempts to answer this question have focused attention on the free evolution of an excited molecule, treating the excitation and the evolution processes as separable. These analyses, and the various experiments carried out to date, lead to the conclusion that, because of rapid intramolecular vibrational redistribution, laser induced selectivity of reaction is not, in general, feasible. In this short paper we show that, despite dephasing of a prepared vibrational state distribution, selectivity of chemical reactivity can be achieved by use of coherent two-photon processes. The problem of finding the optimum waveform (i.e., coherent pulse sequence) that will maximize the formation of a desired chemical species is formulated as a problem in the calculus of variations, and solved for two different cases.