Electron scattering studies of NO2 radical using R-matrix method

Abstract

Nitrogen dioxide molecule plays an important role in modeling atmospheric process. It is a toxic gas and considered as an atmospheric pollutant due to its involvement in reactions that produce ground-level ozone. The electron scattering of NO2 molecule has been extensively studied, specifically at intermediate and high energies. The discrepancies between previous theoretical studies and experimental data at low impact energies (below 4 eV) suggest that the in-depth research should be carried out. The target optimized equilibrium geometry is computed at the highly accurate coupled cluster singles, doubles and perturbative triples[CCSD(T)] level in this study. The ab initio R-matrix method is employed to study the integral and momentum transfer cross sections of low-energy electron scattering from NO2 radical up to 10 eV. Two models including static-exchange and close-coupling approximation are used to reveal the dynamic interaction. The electronic excitation cross sections are computed from ground state to seven electronically allowed excited states. All target states whose vertical excitation energies are below 20 eV are included in the close-coupling expansions of the scattering system. In our CC model, six electrons are in the core orbitals 1a1, 2a1 and 1b2, and the remaining 17 electrons are free to occupy the 4a1, 5a1, 6a1, 7a1, 1b1, 2b1, 3b2, 4b2, and 1a2 orbitals. The aug-cc-pVTZ dunning basis sets are used to optimize the target structure and electron scattering. A Born closure procedure is used to account for the contribution of partial waves higher than l=4 to obtain cross sections. Two shape resonances found at 0.76 eV and 1.82 eV in this study are lower than previous theoretical calculations, but the comparisons with other theoretical calculations and experimental data show that the present R-matrix study not only agrees well with the experiments but also corrects the overestimations of total cross sections of some other theoretical data in the very low energy regions. To study the influence of electron correlations, 21, 82 and 107 target electronic configurations are used in the close coupling model calculations, respectively. The comparisons of integrated cross sections indicate that it is very important to include more target electronic configurations to obtain the converged scattering cross sections, which reveals the importance of electron correlations.