X-ray diffraction analysis: A brief history and achievements of the first century

A DFT/B3LYP method using the 6-311++G(3df) basis set is employed to calculate the geometric, electronic, and thermodynamic parameters of O=NO-ON=O peroxide as an isomer of N₂O₄ dinitrogen tetraoxide. Calculations of the configuration interaction in a system of three paramagnetic particles with open shells have shown for the first time that the formation of cis-cis peroxide in the oxidation reaction of nitrogen oxide 2NO (²Π) + O₂ (³Σ_g) → O=NO-ON=O (¹ A) proceeds without an energy barrier in accordance with recently performed studies. The molecular orbital scheme of the barrierless activation of molecular oxygen and the driving force of the NO oxidation reaction are considered. A spontaneous character of the process is based on the idea of spin-catalysis when the reaction proceeds in the two-triplet state with total zero spin. The obtained results are in agreement with the experimental data on a spontaneous and irreversible process characterized by the observed negative activation energy.