Quantum Chemistry of Nitric Acid: Electronic Structure and Reactivity of Its Decomposition Products

摘要

In the review modern achievements in quantum chemical researches of electronic structure and reactivity of nitric acid (HNO3) and products of its decomposition (nitrogen dioxide-NO2, nitrogen trioxide-NO3, dinitrogen tetraoxide-N2O4 and dinitrogen pentaoxide-N2O5) are considered, (i) Based on the density functional theory (DFT) within the B3LYP/6-311++G(3df,3pd) methodology, quantum chemical calculations of the electron structure, geometry, and thermodynamic parameters of eight isomers of nitric acid (three known isomers in the form of peroxynitrous acid ONOOH and five new isomers in the form of oxo-conformation OON(H)O) are presented. The decomposition of HNO3 on intense heating proceeds according to the general reaction: 2HNO3<->N2O5+H2O, and activation energy of the thermal decomposition of HNO3 is determined by the dissociation reaction: N2O5 → NO2 + NO3. (ii) It is shown, on the basis of a comparison of the calculated and experimental vibration spectra of N2O5, that dinitrogen pentaoxide exists in the gas phase as an equimolecular mixture of N2O5 molecules with Cs and C2 symmetry, while in the solid phase it is characterized by the C2 molecular structure, (iii) Results of quantum chemical DFT calculations with a symmetrized Kohn-Sham formalism of electronic structure and thermodynamic parameters of molecule NO2 in the various electronically excited states (~2B2, ~2B1; ~2A2, ~2A") are analyzed, (iv) It is shown that electronically excited NO2(~2A") molecule, generated by visible light (A.=420 nm), can react with water vapor to produce OH radical: NO2(~2A") + H2O(~1A1)→OH(~2Π) + HONO(~1A'). (v) The results of the DFT/B3LYP/6-31l++G(3df,3pd) calculation of the excited states of NO3 well agree with the experimental data and precise ab initio calculations. The reactivity of high-energy nitrogen trioxide NO3 (~2A1) in the oxidation of N2 and N2O is analyzed. The oxidizing ability of nitric acid is second to none. Thus ten years ago, the Russian chemist M. Karavaev has succeeded in the oxidation of chemically inert molecular nitrogen in nitric acid vapors at temperatures of 758-1173K.