A new approach to molecular classical optimal control: Application to the reaction HCN→HC+N

We present a new method for classical control theory of Hamiltonian systems. This approach is based on a special treatment of the adjoint or Lagrange multiplier equations of motion. The latter function is only asked to preserve the mean of the ensemble of molecular trajectories. In the present case only four such equations are involved greatly simplifying the field design process and making it faster and more stable. Good results are obtained for the selective photodissociation of HCN. The objective is to control the intramolecular reaction HCN→HC+N (i.e., break the stronger bond). Hamilton's equations of motion are employed to model the HCN molecule, initially in its ground state. The control equations are integrated to obtain a high degree of selectivity in the unimolecular dissociation. The robustness of the results to changes in the initial conditions and pulse durations are investigated. An increase of the pulse duration beyond a certain point makes it more difficult to dissociate the N atom due to strong intramolecular coupling. The resultant pulse fields may serve as a basic indicator for future experimental selective dissociation of HCN→HC+N using high power lasers.