Strong field quantum control of bimolecular reactions

Abstract

We present a strategy for the quantum control of polyatomic bimolecular reactions using moderately intense, long-pulse laser fields. Bimolecular reactions pose a challenge to quantum control, not encountered in the unimolecular case, due to their complex scattering dynamics and the averaging of their observables over a thermal distribution of reactant states. Our approach bypasses these hurdles; it involves the interaction of a nonresonant, polarized field with the molecular coordinate-dependent polarizability tensor to generate spatially nonuniform Stark shifts of the potential energy surfaces. We focus on the commonly encountered case where the reaction dynamics involve complicating features such as several coupled electronic states, deep potential wells, a high density of vibronic states, and several transition states en route from reactants to products. We consider highly averaged observables, including the canonical and microcanonical rate constants. It is shown that the complexities of polyatomic bimolecular reactions introduce new opportunities for reaction enhancement and control. In particular, the occurrence of one or more potential wells combines with the spatial structure of the polarizability tensor to introduce a vast enhancement that is subject to control by the choice of field parameters. Our results are based on a quantum mechanical theory and ab initio calculations of the potential energy and polarizability tensor. As a model system, we consider the CH(X2Π)+N2(XΣg+1)→HCN(XΣ+1)+N(S4) reaction, but our results and conclusions are general.