A detailed test study of barrier heights for the HO 2 H 2O O 3 reaction with various forms of multireference perturbation theory

Abstract

We report an ab initio multireference perturbation theory investigation of the HO 2 + H 2O + O 3 reaction, with particular emphasis on the barrier heights for two possible reaction mechanisms: oxygen abstraction and hydrogen abstraction, which are identified by two distinct saddle points. These saddle points and the corresponding pre-reactive complexes were optimized at the CASSCF(11,11) level while the single point energies were calculated with three different MRPT2 theories: MRMP, CASPT2, and SC-NEVPT2. Special attention has been drawn on the intruder state problem and the effect of its corrections on the relative energies. The results were then compared with single reference coupled-cluster methods and also with our recently obtained Kohn-Sham density functional theory (KS-DFT) calculations [L. P. Viegas and A. J. C. Varandas, Chem. Phys.,10.1016/j.chemphys.2011.04.022 © 2012 American Institute of Physics.