By Daiqian Xie
Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
While photodissociation has been extensively studied in the past, new experiments have revealed more details of the dynamics. For example, Yang and coworkers have recently employed the high resolution H-Rydberg tagging technique to measure product state-resolved differential cross sections for the photodissociation of H2O. While providing the most detailed information about dynamics, state-to-state DCSs in polyatomic photodissociation have seldom been calculated quantum mechanically, despite the existence of the photodissociation theory for more than 30 years. Recently, we developed a new set of non-adiabatically coupled potential energy surfaces for the lowest two 1A′ states of H2O at the internally contracted multi-reference configuration interaction level with the aug-cc-pVQZ basis set [1,2]. Quantum dynamical calculations carried out using the Chebyshev propagator yield absorption spectra, product state distributions, branching ratios, and differential cross sections, which are in reasonably good agreement with the latest experimental results. Besides the non-adiabatic pathway by conical intersections between the B and X states of H2O, there is another non-adiabatic pathway by the Renner-Teller coupling between the B and X states near linearity. To investigate the dissociation dynamics involving all three electronic states, a set of coupled diabatic PESs has been determined. We performed state-to-state quantum dynamics for the photodissociation of H2O in its B band involving both non-adiabatic pathways in addition to the adiabatic pathway leading to the excited OH(A) fragment[3,4]. Our dynamical results indicate that, although the Renner-Teller non-adiabatic pathway plays a relatively minor role in the dissociation, the inclusion of all three electronicstates is necessary to resolve the fine-structure population of the OH(X) fragment.
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