A new two-step procedure for laser control of photodissociation is presented. In the first step of the procedure, we show that control of photodissociation product yields can be exerted through preparation of the initial wave function prior to application of the photodissociation field in contrast to previous laser control studies where attention has focused on the design of the field which induces dissociation. Specifically, for a chosen channel from which maximum product yield is desired and a given photodissociation field, the optimal linear combination of vibrational eigenstates which comprise the initial wave function is found using a straightforward variational calculation. Any photodissociation pulse shape and amplitude can be assumed since the Schrödinger equation is solved directly. Application of this method to control of product yields in the photodissociation of hydrogen iodide is demonstrated. The second step of the control procedure involves the preparation of the coherent superposition of discrete levels obtained from the previous step; design of the preparatory field can be done analytically for two or three level systems as demonstrated here or with other well-studied iterative field design methods.

A new scheme for controlling photodissociation through preparation of a variationally optimized linear superposition of field-free vibrational eigenstates is applied for selective control of IBr photodissociation. The dependence of IBr photodissociation on various field parameters and initial conditions is explored. In a broad range of field parameters, the product yield is shown to increase considerably when a photolysis pulse is applied to the variationally optimized linear combination as opposed to photolysis of IBr with the entire population in a single vibrational level. The frequency, intensity, and phase dependence of this enhancement is explored for both CW and Gaussian pulses.

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