Preparing Superposition States to Modify the Spectra and to Achieve Complete Selectivity in Photodissociation...

We derive and apply the geometric optimization methodology to modify the photodissociation spectra of CH₃I in the A band. For this purpose, we prepare optimized initial wave functions that maximally exploit interference-induced coherent control to drive a reaction mediated by nonadiabatic couplings in a polyatomic molecule essentially from the beginning. By designing functionals that maximize the output of the products, or that imply competition between the products, or discrimination of one of them, we test the performance of the methods and the effect of preparing initial vibrational coherences among CH₃-I stretching vibrational states, CH₃ vibrational states, or both. Our results show that using weak ultrashort pulses, one can easily increase the efficiency of the reaction toward any of the products by 100-200% using vibrational states related to the reaction coordinate; that one can increase the efficiency by more than 100% and at the same time almost completely quench the output of products in the other channels. Finally, if one demands high selectivity in the reaction, we show that it is possible to suppress even the most dominant channel to less than one part in a million by preparing superpositions of all available vibrational states optimized with the proper functional.