Full-dimensional diabatic potential energy surfaces including dissociation: The ~2E″ state of NO_3

摘要

A scheme to produce accurate full-dimensional coupled diabatic potential energy surfaces including dissociative regions and suitable for dynamical calculations is proposed. The scheme is successfully applied to model the two-sheeted surface of the ~2E″ state of the NO_3 radical. An accurate potential energy surface for the NO_3~- anion ground state is developed as well. Both surfaces are based on highlevel ab initio calculations. The model consists of a diabatic potential matrix, which is expanded to higher order in terms of symmetry polynomials of symmetry coordinates. The choice of coordinates is key for the accuracy of the obtained potential energy surfaces and is discussed in detail. A second central aspect is the generation of reference data to fit the expansion coefficients of the model for which a stochastic approach is proposed. A third ingredient is a new and simple scheme to handle problematic regions of the potential energy surfaces, resulting from the massive undersampling by the reference data unavoidable for high-dimensional problems. The final analytical diabatic surfaces are used to compute the lowest vibrational levels of NO_3~- and the photo-electron detachment spectrum of NO_3~- leading to the neutral radical in the ~2E″ state by full dimensional multi-surface wave-packet propagation for NO_3 performed using the Multi-Configuration Time Dependent Hartree method. The achieved agreement of the simulations with available experimental data demonstrates the power of the proposed scheme and the high quality of the obtained potential energy surfaces.