Photodissociation of HI and DI: Polarization of Atomic Photofragments

Abstract

The complete angular momentum distributions and vector correlation coefficients (orientation and alignment) of ground state I(²P_3/2) and excited state I(²P_1/2) atoms resulting from the photodissociation of HI have been computed as a function of photolysis energy. The orientation and alignment parameters, a_Q^(K)(p), that describe the coherent and incoherent contributions to the angular momentum distributions from the multiple electronic states accessed by parallel and perpendicular transitions, are determined using a time-dependent wave packet treatment of the dissociation dynamics. The dynamics are based on potential energy curves and transition dipole moments that have been reported previously [R.J. LeRoy, G.T. Kraemer and S. Manzhos, Journal of Chemical Physics 117, 9353 (2002)] and used to successfully model the scalar (total cross-section and branching fraction) and lowest order vector (anisotropy parameter B) properties of the photodissociation. Predictions of the a_Q^(K)(p), parameters for the isotopically substituted species DI are reported and contrasted to the analogous HI results. The resulting polarization for the corresponding H/D partners are also determined and demonstrate that both H and D atoms produced can be highly spin polarized. Comparison of these predictions for HI and DI with experimental measurement will provide the most stringent test of the current model for the electronic structure and the interpretation of the dissociation based on non-coupled excited state dynamics.

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