Catalysts are defined as substances which accelerate reactions by lowering the activation energy barriers for selective reaction pathways without being used up in the reaction. Traditionally, these substances can vary from enzymes, to organometallic complexes, to metal surfaces. An intriguing different possibility is to use the strong electric field associated with a pulsed laser to catalyze the reaction such that the photons are never used up in the process, i.e., the laser field is non-resonant with respect to any transitions in the system under study. A simple reaction system for investigating laser catalysis is the photodissociation of hydrogen halides, HX. These systems have been investigated thoroughly, both experimentally and theoretically, and provide a model for a 1-step reaction involving an excitation from a ground state to an electronically excited potential energy surface. In the case of hydrogen halides, excitation onto repulsive electronic energy surfaces results in instant dissociation of the molecule into different channels, either through direct excitation to the respective surfaces or through non-adiabatic coupling between energy surfaces. By applying a strong laser field, it is possible to alter the dissociation dynamics, as surfaces with different polarizabilities are expected to interact differently with the field, thereby altering their relative energies and the probability of non-adiabatic hopping between surfaces. Particularly for HX systems, two dissociation channels arising from the spin-orbit interactions produce X in its ground state and the spin-orbit excited state of X (denoted by X*). The ratio of the reaction cross sections for these two channels is referred to as the branching fraction. In the present study, the effect of an applied electric field on the dissociation dynamics of HBr photodissociation is investigated by following the change in the branching ratio in comparison to that observed for non-field photodissociation. The effect of the electric field on the branching fraction will be investigated in terms of excitation wavelength, intensity of the electric field, and polarization of the electric field. Results of this study will provide information on which mechanisms for dissociation are more sensitive to the stark perturbation associated with application of the electric field.

Effect of the application of a non-resonant electric field on the photodissociation dynamics of HBr

253rd National Meeting (2017)

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