Control of transition state spectra: a variational algorithm

We propose to control the characteristics of transition state spectra by de signing the initial state of a photochemical reaction. The method proceeds by introducing parameters into the (nonstationary) initial state wave funct ion. The parameters are determined variationally to optimize a desired feat ure of the spectrum. One important application of this procedure is to redu ce the unstructured background in a photoabsorption spectrum. In the result ing spectra, the contrast ratio of the resonance peaks to the background is dramatically increased, allowing a spectral quantization procedure to be u sed to assign the peaks. The algorithm can also be used to resolve overlapp ing peaks and to enhance specific progressions. As a theoretical tool, the variational algorithm can be viewed as a method to analyze the resonance st ructure of a given potential surface. We speculate that control of spectra can also be achieved in the laboratory, and suggest one possible scheme to do so. (C) 1999 Published by Elsevier Science B.V. All rights reserved.