Global analytical potential energy surfaces for HO₂(X̃ ² A″) based on high-level ab initio calculations

Two global analytical potential energy surfaces for the H O2 (X̃ A″2) system have been developed by fitting ∼15 000 ab initio points at the icMRCI+Qaug-cc-pVQZ level of theory, using the reproducing kernel Hilbert space method. One analytical potential is designed to give a very accurate representation of the low energy range that determines the vibrational spectrum, while the other attempts to provide a fast and uniformly accurate potential function for reaction dynamics. The quality of the fitted potential functions is confirmed by good agreement of the (J=0) H O2 vibrational spectrum and (J=0) quantum reaction probability for the H+ O2 (ji =0, i =0) reaction with those obtained using the spline fitted potential. Quasiclassical trajectory calculations carried out on the new potential energy surface provided the reaction probability with a zero impact parameter (b=0), which is in reasonably good agreement with the J=0 quantum results.