Control of transition state spectra: a variational algorithm Original Research Article

We propose to control the characteristics of transition state spectra by designing the initial state of a photochemical reaction. The method proceeds by introducing parameters into the (nonstationary) initial state wave function. The parameters are determined variationally to optimize a desired feature of the spectrum. One important application of this procedure is to reduce the unstructured background in a photoabsorption spectrum. In the resulting spectra, the contrast ratio of the resonance peaks to the background is dramatically increased, allowing a spectral quantization procedure to be used to assign the peaks. The algorithm can also be used to resolve overlapping peaks and to enhance specific progressions. As a theoretical tool, the variational algorithm can be viewed as a method to analyze the resonance structure 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.