The Potential Energy Surface of the H2O2 System

Abstract

The potential energy surfaces (PES) for the singlet and triplet H2O2 molecular system were studied by using the CASSCF, CASPT2, QCISD, QCISD(T), and CCSD(T) methods with the aug‐cc‐pVDZ, aug‐cc‐pVTZ, and 6−311+G(3df,2p) basis sets. The CASSCF and CASPT2 results show some significant differences from the QCISD, QCISD(T), and CCSD(T) calculations. The QCISD(T)//QCISD and CCSD(T)//QCISD calculations were found to be suitable for examining most of the species and reaction paths on the H2O2 PES except for a few open shell species which have a multi‐reference character. The CASSCF and CASPT2 methods were found to be better suited for treating these open shell species. Consistent with previous theoretical and experimental work we find the hydrogen abstraction reaction 1O + H2O → 2OH + 2OH to have a small or no energy barrier suggesting this pathway may have relevance to the astrochemical formation of hydrogen peroxide in an extraterrestrial environment.