Ab initio adiabatic and quasidiabatic potential energy surfaces of lowest four electronic states of the H⁺ + O<inf>2</inf> system

Ab initio global adiabatic and quasidiabatic potential energy surfaces of lowest four electronic (1-4 A3 ″) states of the H+ + O2 system have been computed in the Jacobi coordinates (R,r,γ) using Dunning's cc-pVTZ basis set at the internally contracted multireference (single and double) configuration interaction level of accuracy, which are relevant to the dynamics studies of inelastic vibrational and charge transfer processes observed in the scattering experiments. The computed equilibrium geometry parameters of the bound [HO2] + ion in the ground electronic state and other parameters for the transition state for the isomerization process, HOO+ OOH+ are in good quantitative agreement with those available from the high level ab initio calculations, thus lending credence to the accuracy of the potential energy surfaces. The nonadiabatic couplings between the electronic states have been analyzed in both the adiabatic and quasidiabatic frameworks by computing the nonadiabatic coupling matrix elements and the coupling potentials, respectively. It is inferred that the dynamics of energy transfer processes in the scattering experiments carried out in the range of 9.5-23 eV would involve all the four electronic states. © 2010 American Institute of Physics.