Control of transition state spectra: Enhancement of diffuse structure in the photodissociation spectrum of CO2

The photodissociation spectrum for collinear CO2 is assigned using the spectral quantization method. The diffuse structure in the spectrum is dramatically enhanced through the use of a newly developed control algorithm. An initial state is variationally designed to suppress the broad direct background, which usually dominates the spectrum, while it simultaneously enhances the intensity of the resonance peaks. All the diffuse structure can be attributed to resonance states trapped near the saddle point. Using time-independent wave functions, which are extracted by Fourier transforming the wave packet at the frequencies of the spectral peaks, the spectrum is assigned to an assortment of Feshbach and barrier resonances built on the asymmetric and symmetric stretch modes, The influence of periodic orbits on the diffuse structure is also assessed. (C) 1996 American Institute of Physics.