Theoretical studies on HOONO, HONOO, and HNO3 isomers and their isomerization reactions

The energies and structures of various peroxynitrous acid (HOONO), HONOO, and nitric acid (HNO3) isomers as well as their isomerization reactions have been investigated at the CCSD(T)/6-311+G(2df,p)//B3LYP/6-311+G(d,p) level of theory. Three HOONO, four HONOO, and one HNO3 isomers are found here. Among them, the trans-trans and cis-trans HONOO configurations are new isomers. The HNO3 conformer is the lowest in energy among all the isomers, HOONO conformers are relatively higher than HNO3, and HONOO conformers are energetically the highest. It is shown that different isomers of HONOO can rearrange into each other, so can HOONO isomers. Moreover, the isomerization reactions of HOONO and HONOO into HNO3 are observed. The computational results show that these conversions can proceed through both concerted and stepwise mechanisms. Additionally, the effects of aqueous solvation of water on the isomerization reactions are also investigated.