A novel mechanism for the isomerization of N2O4 and its implication for the reaction with H2O and acid rain formation

Raghunath Putikam, Ming-Chang Lin*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


We have discovered, by high-level quantum-chemical calculations, a new and predominant isomerization mechanism for N2O4 → ONONO2 via a roaming-like transition state occurring unimolecularly or bimolecularly during collision with H2O. The new mechanism allows N2O4 to react with H2O with a significantly lower barrier (< 13.1 kcal/mol) than the commonly known tight transition state (∼30-45 kcal/mol) by concurrent stretching of the NN bond and rotation of one of the NO2 groups to form trans-ONONO2, which then undergoes a rapid metathetical reaction with H2O in the gas phase and in aqueous solution. The results have a significant implication for the hydrolysis of N2O4 in water to produce HONO and HNO3. Rate constants for the isomerization and hydrolysis reactions have been predicted for atmospheric modeling applications.

Original languageEnglish
Article numbere25560
JournalInternational Journal of Quantum Chemistry
Issue number12
StatePublished - 15 Jun 2018


  • HONO and HNO formation
  • NO hydrolysis
  • NO isomerization and reaction
  • roaming-like transition state

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