Optimal control of unimolecular reactions in the collisional regime

Abstract

The possibility of controlling unimolecular–dissociation processes with multiple laser fields in the collisional regime is examined. Employing the Bloch equations to describe optical excitation and decay processes, optimal control theory is used to design amplitude modulated fields which produce the desired excited‐state products. The selectivity of the product distribution of a simple four‐state photodissociation system is shown to have a square‐root dependence on the relative value of the mean dephasing time T 2 to the pulse length τ, i.e, (T 2/τ)1/2. The equivalence between T 2 decay and phase disruptions occurring in a random‐walk fashion is also examined. In the Appendix it is shown that the essential effect of the system temperature is to introduce a Boltzmann population factor on the product selectivity without affecting the nature of the optimal field.