Optimal control of selective vibrational excitation in harmonic linear chain molecules

A formalism for designing an optical field for selective vibrational excitation in linear harmonic chain molecules is presented based on optimal control theory. The optimizing functional producing the field designs is flexible to allow for the imposition of desirable laboratory and theoretical constraints. The designed optimal fields, which successfully lead to local bond excitations, exhibit complex structure on the time scale of 10 fs. Analysis of the optimal fields shows a high degree of cooperativety between the temporal structure of the fields and the dynamical capabilities of the molecules. It is generally impossible using only spectral information to devise the optical field needed to selectively excite a local bond in a polyatomic molecule. These results explain why the previous intuitively based laboratory attempts at site specific chemistry have yielded disappointing results.